I recommend a M203 Grenade Launcher on the lower rail attachment. Just in case you run into a street gang or the in-laws drop in unannounced and want to hang out for the weekend.
I've been using Sportsman's Guide for ammo, but the few things they have in stock are priced through the roof.... $10 for 50 rds of .22! .38 and .357 FMJ are damned near impossible to find on there. I'll check out Doubletap. Thanks!
Try AIM Surplus for ammo. Best prices around. Just get on their email list if the ammo is out of stock. they will send out flyers when it comes back in stock.
Double Tap is expensive.