You might be best off looking in (you need an account to see links)!
I know I saw one for sale somewhere, but it was up above $150. People may lend theirs for the avatar, but those who are selling them seem to be far and few between.
Alternatively, there's a handful of decent BD guides (you need an account to see links), under "Battledome Guides". There's a couple of general guides as well as ideas and lists for battle sets.