20 gauge defense barrel and buckshot choke.

[Okie1297]

I have a 20 gauge 870 and I want to get some buck shot for it for home defense and messing around on the range. My question is, is there a 18-20” barrel for 20 gauge 870s? I tried looking and haven’t found any if I can’t find one what choke is best for buckshot? I plan to get a 12 gauge Mossberg hd gun when I turn 18 but I still want to use my 870 as much as possible.