Decide which route you want to take, by Trust or the complicated way (fingerprints, signed by LEO and photographs). Either way use form 4, $200 money order and 6 months of waiting.
I chose the Trust way. I'm still waiting for the Tax Stamp to gets back. Hopefully sometimes in September. It's the YHM Phantom 3500 SS QD. It costed me <$600.
Check out your local Class 3 dealers or silencershop.com (Dave). He is a nice guy to deal with.