"Stock blocks" are the most common method. You use a G36 trigger housing, put the SL8 FCG in there, and then attach some type of stock. Blocks were/are available to adapt to ACR, G36 and AR15 styles. The G36 stock block gives you the most authentic G36 look.
Then there are the dedicated new lowers like Tom's PSG8, and the Hera Arms kit. The Hera kit gives you the most flexibility in choosing a stock, because it allows the ACR stock, or any AR15 stock. The AR15 ACE adapter can be used to bolt on any ACE-compatible stock, of which there are many.