Lens boards are good candidates for internet purchase, because they are relatively small and easy to ship.
One thing that you need to understand is that enlarger lenses have threads at the back which are used to attach the lens to the board/plate/mount that the enlarger uses. The sizes of those threads vary, although 39mm is very common.
Some boards/plates/mounts are threaded, but most have a hole which the lens threads pass through. The latter setup requires that you also have a retainer ring/jam nut to thread on to the back to hold the lens to the board/plate/mount.
Retainer rings/jam nuts are also good candidates for internet purchase.