The market price is basically an average of all the buy and sell prices. This means that if you buy at an exchange with really high daily volume you'll basically buy at a price very-very close to "market price" (you can say that you've bought at market price). The only problem is that you may have to also pay various fees (especially at centralized exchanges).
So, as already said P2P platforms may be your best choice.

Of course, you may find sellers on the forum too, but you'll have to be careful (not all are honest) and you'll have to also offer non-reversible payment (since you are new and nobody knows you). In this case you'd probably have to tell clearly the amount you are interested in, method of payment, maybe website of choice to decide the price and... use the Currency Exchange subforum (as also said).