The original flash bulb-type flash attaches to the bayonet mount of either the taking or viewing lens and takes a funky (but still available 22.5 volt battery). I do believe the MX is a Bay 1 size; there is 1, 2 and 3 for Rollei TLR cameras.
Most sellers on Ebay are clueless as to what size they have, so be prepared to be disappointed unless they specify which size attaching arm comes with the flash gun. Of course, the flash head unscrews from the attaching arm, so any size Bay adapter can be used with the flash gun, but finding the right size took me about three purchases. Luckily I have Rolleicords that work with my "failed" attempts.
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Rollei did make a strobe version of this unit, but they are harder to find and the electronics are getting quite old, so they can be a gamble for reliability.
Of course, you can use a common flash bracket in the tripod screw and have the flash "outboard" on a hand grip, but you will have to purchase a Rollei flash terminal adapter as it is not a standard PC connector on the camera.
The easiest option would be to purchase a Rollei flash terminal adapter and use a bracket mount "potato-masher" style press strobe like the Sunpak or Metz variety. The added bonus is auto exposure on some dedicated models of these strobes with the right set-up.