Yes, you can get MATIC from Coinbase. That's where I got mine. Your other option is to use LEO. You can wait for PolyCUB to launch, bridge some LEO over to pLEO, and then swap some of that pLEO for MATIC on the PolyCUB platform.

I put like 150 MATIC into my Polygon Chain metamask wallet by getting it from Coinbase, but I will also be using some pLEO to get some more (if I want to pool it with MATIC) once it launches.

That said, when I moved my MATIC from Coinbase to metamask, I ended up sending it to my Ethereum wallet rather than my Polygon wallet. It gave me a few nervous moments trying to figure out why it didn't show up. I ended up having to "bridge" it over from the ETH chain to the Polygon chain. It wasn't difficult but it probably cost me a few dollars. Just thought I'd point out what happened to me in case anyone else runs into the same issue.