Using BJT's with a 595 shift register not outputting expected current.

CrossRoads:

The issue was that I was indeed running out of pins.

Then go with TPIC6B595 controlling PNP transistor, P-channel MOSFET.
Or as input to UDN2981 or UDN2982 if you can find anyone that still sells them:
http://www.digikey.com/product-search/en?lang=en&site=us&KeyWords=udn2982

Can’t go the TPIC route, it needs 4.5V to 5.5V input, teensy runs off of 3.3V in. Should the NPN route not work?

Ok, then 74HC595 with NPN as buffer to pull PNP base low, and pullup resistor to 12V to drive PNP base high.
Or P-channel MOSFET, with NPN to pull gate low, and pullup resistor to 12V to pull gate high. Use a Low Rds part to minimize heating and voltage drop across the part.
These are the lowest priced well <1 ohm resistance parts

http://www.digikey.com/product-detail/en/NDP6020P/NDP6020P-ND/1055922
http://www.digikey.com/product-detail/en/SPP15P10PL%20H/SPP15P10PL%20H-ND/2783608

Thanks so much for your help thus far. I'll be testing all suggested approaches this weekend and will report back with hopefully some good news.