I trade on Schwab and TDA. I have traded in at least 5 CE stocks for buys on Schwab this month. I have only tried TDA with GBDX and it was restricted. Due to the fees TDA charges for penny stocks, I usually don't trade them there. Just did a test on GBDX which I have no trouble buying or selling on Schwab.
EDIT have done buys with Schwab for these CE plays DBMM, ECCI, PMDP, SFIN,GBDX, TRAE.