CMMG makes a good conversion. The market is full of magazines for them too. The conversion package that comes with three magazines costs around $300 and some change.

To be honest, you can actually find dedicated 22lr uppers for just about that price. Complete with BCG and charging handle. A much better deal IMHO than the conversion kit which is basically just a BCG and mags since .22 doesn't like the 1:7 twist rate. And yes, the gas tube will foul up a lil quicker with the conv kit.

HTH