I use Minolta flashes (5600HS(D)) with my RZ. What you need is an FS-1200 (generics are available for ~$10 on eBay) hotshoe adapter for each flash. You can either plug the flash (with FS-1200) straight into the camera's hotshoe, or you can use any old cheap RF trigger kit between the RZ and the flash. I can sync reliably at 1/400 with the Minolta flashes and cheap Cactus-II (otherwise known as Yongnuo or Phoshot, with 4 channels) RF triggers.

Flash power will be manual with that setup.

If you want to be very fancy, you can get a Metz SCA adapter for the RZ and have auto-flash using control from the camera. You can also get auto-flashes (where the metering is in the flash using a cell on the front) to work with the RZ but you need to set the ISO and f-stop on the flash to match camera settings.

Edit: I get about f/5.6 light from a 5600HS(D) at full power, bounced from an average height white ceiling. That's OK for portraits with ISO400 film at f/11 but is insufficient for slower/finer film (f/2.8 at ISO25, d/oh!). As direct flashes, the Minoltas are powerful enough for fill in full sunlight at typical portrait ranges.