[Shotimes] Brake bias plug question

[Jon Heese]

I know this runs into vendor interference territory and I don't want to 
step on any toes, but I couldn't help but wonder and I don't think I've 
heard anyone mention it before now:

The rear brake bias valve plugs seem to be a really low tech solution to 
the problem of weak rear braking due to SLO parts crossover.  What I 
mean by this is that they appear to simply be a pair of threaded brass 
plugs with a pair of o rings.  Is there any magical reason why they run 
between $30 and $50 from the SHO vendors?

Is the plug rare enough to warrant these prices?  Unless I'm missing 
something, it seems like this should be a hardware store item (or maybe 
a mcmaster.com item) with publicly available thread/size specs, but 
every mention of the technique seems to indicate that the only place to 
get them is from a vendor.

Regards,
Jon Heese