Run, do not walk, run to your local Target. They have Umbaran MHC polybags in the Hallowe'en section. They are $3.99 for 49 pieces, which is $0.08 per piece. You also get something that looks a lot like an Ijad Scrambler in one bag.
Also! Over on the Hangar, darksyntax has reported that black Travis bricks can be found on the Pick-A-Brick Wall. That got your attention? :-)