I converted my cable park to a USB-C cable (male to male) and lots of adapers (the short sort you can keep in a box) years ago. Yet i have still some devices with a mini-B female port.
Only thing i found online are cables and everything else. Heck, there's even mini-DP > C and ethernet > C in that form factor.
To clarify, i look for something like this but mini-B instead of micro.
edit: Region is Swiss, Europe.
editedit: thanks guys, found one.
When clicking that link it came up with the last time I've purchased it. So as a random Internet stranger I can actually vouch for these.
I've got an old Sonicare travel toothbrush that used that as a charger and really didn't want to pack another cable. I've bought another pack because I ended up giving one away to a friend that lost the cable for a digital camera they use for work, and cannot use their cell phone for compliance reasons.
In both cases it has worked fine for just charging, and for data transfer.