Here in my place, there is an over-the-counter transaction for purchasing large volumes of BTC. But I prefer a peer-to-peer transaction. That would be the best choice. That would be much safer in terms of protecting your identity. I guess you are avoiding doing the purchase through exchanges for the same purpose. 

Here: https://bitcointalk.org/index.php?board=53.0. This is the section where you might want to post your terms and offer.

Here in my country, there are now many licensed and legit Bitcoin selling and buying platforms which are operating under the category of money remittance business. It is quite easy to buy a volume of Bitcoin but of course you need to coordinate with them as the transaction is not the usual one and if you do it one time then you can be reported to the Anti-Money Laundering Council as specified by the law. Since these are licensed, the rates are usually higher than what one can find in the P2P market but then this can be less risky than finding someone else to trade (except if you know that somebody, of course).

In trading, especially in the stock market, besides price data there is also volume data. If prices are the main focus of traders in analyzing, this is not the case with volume. Volume is often forgotten. Many traders do not use volume in their analysis. They do not understand the meaning of volume and only see the volume indicating the market is crowded or quiet. What is the volume? How to read the volume correctly and apply it?
What is volume? Volume can be defined as the number of shares or contracts on a stock or on all shares in one stock traded in a certain period. In other words, every time a share is bought or sold by someone, this is the volume. to more clearly visit this site https://coinmarketcap.com/ there we can see the transaction volume per 24 hours, logically the transaction volume is the buy sell that has occurred and bring up the latest price.

How large volumes do you mean?

Localbitcoins are cash trades are no longer a thing. I think 1-2 months back, they were forced to remove it due to legal issues (specifically from the EU and Finnish government), but I am not 100 percent sure. Localbitcoin traders may still do OTC though, just DM large sellers on the site that are close to your region and ask them for a cash trade, there won't be an escrow though, so keep this in mind and set a safe and public meeting location.

For other marketplaces/OTC, I can recommend sites like OTCBTC, Bittrex, other marketplaces. Keep in mind, doing a large transaction for cash will likely mean that your seller will ask for your ID and other items.

For those who want to buy a lot of BTC, they mostly buy it OTC (Over the counter). Institutions never buy btc from exchanges. I am curious to know how many BTC do you want to buy ?

I have never done a large number of BTC buyers, because in my country depositing cash to the stock exchange is very difficult,

Depends on how large in volume it is. Even verified accounts in exchanges sets a limit on the amount you can buy. Again, exchanges are also never reliable. You best bet is to find someone will to sell BTC and do a peer to peer transaction. Safest and the most easiest way. A single person might not have all the BTC you need, but you can buy from several people.
Just go for p2p transaction. No hassle, safe and no extra bullshit fees.

So you have considerable amount of physical cash with you, and you want to convert them to cryptocurrency? You can try your luck by posting your proposal in the Currency exchange sub-forum (https://bitcointalk.org/index.php?board=53.0). But I am not sure whether anyone will deal with you or not, since you are quite new to this forum, and don't have any reputation.

There are multiple risk factors associated with selling BTC for physical cash:

1. There is a chance that the money is not clean. In that case, the authority can arrest the buyer and trace his BTC back to you.
2. Personal deals (face-to-face) are not encouraged, as there have been multiple incidents of fraud.
3. If the volume of the physical cash is large, then the seller is vulnerable to raids from the authorities.

There is no limit to how many coin of btc you can buy since you have your funds and getting it from a good exchange or reliable source then you have no worry to think about , just be very careful with your wallet key and play save with it since it has a very huge amount in the wallet.