Well, I'm not an expert at procurement or anything, but I'll offer my best guess, to help you out.
I know lots of times stores are out of stock on items, including things like pressure washers.
Let's say the Quality Control on wands is really bad for a while, but Simoniz doesn't care, because the stores agreed to never, ever give a customer a refund or exchange.
So, there would be a 'run' on those replacement parts, so stores would have trouble keeping them in stock.
There sure are a lot of complaints about these Simoniz pieces of junk, on other sites, but also on the most-popular thread on this site:
https://www.canadiantiresucks.net/personal-stories/68-simoniz-scam.html
That's just one example.
Or maybe Simoniz really is a messed up company (for example), and can't make enough spare parts for all their screw-ups. Or else they just aren't any good at filling orders for spare parts. That would explain it.
One more idea.
Maybe our American friend bought it a while ago, and it was one of the few units that actually survived a few uses. Then maybe the crappy warranty on the crappy pressure has run out, so he's trying to get old parts for an old model, that isn't really stocked anymore.
Ok, Hope that helps!
Anything else on your mind? 'Bring it on!'