Cabela's shows HSM Bear Load ammo in 45-70 as being in stock. They don't list a velocity but HSM are usually pretty hot.
h ttp://www.cabelas.ca/product/35609/hsm-bear-load-ammunition
Over on the Marlin forums a guy chronied some in a guide gun and got ~1750fps. They're loaded with 430gr hard cast bullets.
The stuff isn't cheap though. For $3/round after tax you can pay for a Lee Loader set pretty quick. A tray of 100 primers, 1lbs of powder, and a box of 100 bullets can save you some money. I know not everyone is interested in reloading but just putting it out there. I've loaded 300gr JHP's up to 2400fps. Some 500gr cast I loaded up to 1400fps and decided to stop since they could go clear through a 14" poplar tree and I figured I would never need more than that for anything in North America.