You can always call airnet. I know that they do have some sort of program where you ride right seat in a baron, chieftain or what have ya and fly the non-rev legs. As far as I know, you need to have all the requisite ratings to participate in the program that they offer. I think Royal Air may do the same as well. Good luck
theres a few.
Wiggins-fed ex feeder
airnow-ups feeder and bank work
island express-out of business finally <schotty equipment>
contract air cargo-i see them up here in the NE
zantop-large freight out of YIP.
theres a few. you do need the usual 135 minimums at least for these jobs..1200 total. 250 xc. be really good with your instruements. bad icing is cool...only till you get in it. it isnt cool any more.