So MATIC tokens can be bought from any centralized (Binance, Coinbase, et.al) or Decentralised (Uniswap, QuickSwap) exchange. You may also research and try some on-ramps like Transak, Ramp. The purpose for your purchase of MATIC coins should also determine where you’ll buy them from and the network. It is advisable to have MATIC on Ethereum Main-net if your intention is either staking or delegation. if your intent is a transaction on the Polygon mainnet, you should hold and transact with MATIC on Polygon mainnet.