1377 barell band and other parts

[bird blaster]

What are the best kind and where to get them? are the plastic ones good from Amazon? I've been adding up the total of my 1377.
1377 free bought with a gift card
Stock-20$
Aim sports 3-9x40 scope. 33$
18 inch barrel ?
Disco bolt ?
 So can you help me come up with the cost and I'm going to buy the rest of the stuff like the barrel and longer bolt from Crosman.i heard every additional inch of barrel is 10-12 fps added on so if mine is shooting 574 fps and 8x10= 80 so I should be shooting 8 grain pellets at about 655 fps. Thanks

[bgmcgee]

Check alchemy airwerks on eBay.  He's a vendor here too. Davio has most of the parts you will need, is a good guy and from others that have bought his 3d printed barrel band I hear it works well. I have a bluefork one from hpa sports and it is a great band but pricy and not always in stock.