There are loads of digi synths available but just a few things to bear in mind, older gear will prob need a battery replacement. Not a big problem providing its not soldered to the board..
Midi controllers for modules are available but not after some searching - these days they tend to be mostly the usb type. Not good for older sound module that have standard midi ports. Computer sequencers are fine but bear in mind depending on your system they dont give rock solid clock timing like a hardware seq gives.