Unfortunately, I've had the same experience. I've given up, at least for the time being, hopes of having a WLF for my SQ-A. Fortunately, though, I haven't really felt the need for one either, just the desire to have one!
Yes, after months of monitoring ePrey last summer, I bought a WLF from KEH. I paid more for the WLF than I paid for the SQ-A body or per back for two of my three backs. But I really do like it for most stuff. I just got an unmetered prism finder for $42, but haven't seriously used it yet.
Datchet, Berkshire UK- about 20 miles west of London
The Bronica wlf came as part of the kit, and tends to be sold on with the camera body. Same with the winder crank. Both of these are fairly scarce used whereas the prisms were almost always bought separately as accessories and are often sold as such. Same with 220 backs and Speedgrips - rarely supplied with a camera, now relatively easy and cheap to find. WLF do sometimes come up in the UK and tend to sell for the equivalent of maybe $80-$100. You need to ask what dioptre they have fitted in the magnifier since these are user interchangeable and its important that you can see well through it.
So the best way to find a wlf ( or a crank) is to buy a camera with them in place and that is by no means difficult. Piecing together a kit from bits is not a guarantee of spending less or a recipe for an easy life. You could be as well off selling your body and buying another with a wlf included.
My own view as a long term Bronica user is that I want to have a spare kit of most of the major bits. Bronicas are cheap right now but repairs and parts are going to get scarcer and more problematical in future. It might well get to be easier and cheaper to replace rather than repair- and this is by no means unique to Bronica and should be considered when choosing which discontinued/used camera to buy into. Here in the UK it would be difficult to sustain a decision to build and maintain an extensive older Rollei MF system, but not too tough on Bronica SQ or ETRS series since the latter sold a lot more. Indeed you might find on any given day that there's about the same no. of Bronica items for sale as in the US.