I repeat, every time something breaks you are going to need to order parts for it from the US or UK (and we are talking down to nuts and bolts), or (expensively) manufacture it yourself. They'd be dockyard queens sitting around doing nothing waiting for repairs. (Which would in fact be excellent practice for the WW2 German surface fleet).
Buy them in the 30s with the stock of spares and ammo the previous owners had. As for nuts and bolts, the Cubans keep those old Buicks running by making a few. I expect there was some small workshop in Germany that could make a few bolts to size....