You could try calling BnD, but really all the parts you are referring to are wear items. Many times you can find larger packs of caps on EBay or Amazon. If you are not opposed to maybe 1 size up on line- that may extend your life. Most of these spools will run .065 with no issue.

i just read the specs on a B&D

Model # ST7700 not sure if that is the one you have? but this 1 say's the spool can hold 30" of .065 line. i'm not sure what's happening with your trimmer but going through 30' of line in 20min? i can put 20' of line on my trimmer and go awhile. i also read it has a self advancing style head. if your happy with the machine they say replacement heads are available, just swap out the hole head.

This is the one I have, and if you read the comments many people complain of the same issues, that's why I thought talking to black and decker would be a good idea?

http://www.homedepot.com/p/BLACK-DECKER-6-5-Amp-Straight-Shaft-Electric-String-Trimmer-GH900/204630526

it looks like there's a problem with the auto advance mechanism? was there any kind of recall? i did read the warranty. it should still be under warranty. i think you missed the home depot return window, so you'll have to contact a B&D service center. could be an opportunity to think about another trimmer. i just sold a stihl fes60 (didn't need). it was impressive.