What kind of cylinder do I need for this type of lock?
You can use a standard mortise cylinder, but it needs the correct tailpiece fitted
Based on the patent you linked (good find!), your lockset does work with a standard mortise cylinder (item 30 in Figure 2).  However, different mortise cylinders accept different styles of tailpieces to interface with different locksets.  While you appear to have the roller (item 36 in Figure 2) that mates with the T-slot (item 63 in Figure 3) in your lockset, the tailpiece (called &quot;cam&quot; by the patent, item 32 in Figure 2) that interfaces with that roller is missing.  Fleetwood may be able to sell you a spare tailpiece if you ask nicely (using the term &quot;tailpiece&quot; for what you're after should help, as tailpieces are commonly needed spare parts in the locksmithing world); if not, you'll have to have one fabricated (it doesn't look like a terribly hard machine-shop job to me, at least, though).  Once you have the correct part, you can simply attach it to the back of the mortise cylinder's core, provided you have a mortise cylinder that accepts two-screw tailpieces (some use a different style).