Does it need a new Output Transformer or a new Power Transformer? Double check this first.
Here are the models of each for the IIC+:
Output
60W OT - T60-152019,
100W T100-152019
Simul Class - SC-152019B
Coliseum 180W - SD 190555
Power
60W PT - 00-162310
60W Export - X62-162318
Early 100W - 100-162318
Simul/60-100 Power - 105-162318
X101 Export -162318
180W Coliseum - 0180322
Some of the Schumacher transformers continued into the Mark III production range and also into the Mark IV but changed their product number. I think there was a thread on here where someone had a Mark IV transformer in theirs which was done by Mesa as they ran out of IIC+ transformers? Also loads of good info here:
http://www.forum.grailtone.com/viewtopic.php?f=3&t=11253
Either way find out EXACTLY what transformer has blown, the EXACT model number you need, and check it definitely has blown and isn't something else wrong with the amp (make sure the rest of it is there!). Then give Boogie a call for advice. You can test these things by using the maintenance manual: http://mesaboogie.com/media/User%20Manuals/Mark%20II-C%20Manual%20-%20Maintenance%20&%20Repair.pdf
It specifically says:
5. Output transformer. If all voltages are correct and good clean drive appears on the 6L6 grids (pins 5)
but not on the plates (pins 3), or on the plates but not at the speaker jacks, the output transformer is
suspect. To verify, use a substitute. Fender transformers (Bassman for 60-watt models, Twin or Showman
for 100-watt models) may be used until original replacement arrives. If Fender transformer is used,
temporarily move feedback over to four ohm jack as Fender transformers have no 8 ohm winding.
So if the Power Transformer is OK it should still power up and get voltage to the valves.
That's the first thing to check to then you can go from there. Shame you don't have the old transformer as companies can cut them open and clone them usually. Mesa should be able to source you with a replacement as close as possible to the original once you know the exact issue.
Let us know how you get on!