If anyone is looking to get rid of capes they are using from their Ultimates, I would buy or trade for:

Shredder's plastic cape
Shredder's soft goods cape and belt
Splinter's soft goods robe and belt
Mumm-ra's soft goods cape (regular or glow in the dark version)

Or if you can sell me Shredder or Mumm-ra at a decent price, I would buy/trade the whole figure off of you.