Don't know of anyone who works on them although there must be someone out there. I have seen 250's and 210's in working order going for $25-30 at hamfests so usually it's cheaper to try to find a used one.
Most have upgraded their systems so the old 250 won't cut the muster. You'd be much better off with one of the newer P25 digital/trunking scanners and reserve a bank for federal. Another good reason is the 250 has the same single conversion receiver board as my old 101 which is prone to bleed over (PLL frequency error) and intermod and doesn't get the narrow band "splinter" frequencies quite right when it rounds off the four digits to three. It has just about the most sensitive receiver ever put in a scanner but too many shortcomings for today's bands.
KEV, if you ever suggest the 210 again I'll crown you! (;->) On the opposite end of the scale it's the worst POS I ever had the misfortune to work with, cheap and dirty (mostly dirty) it was Electra's (Bearcat pre Uniden) worst mistake.
I have 18 BC-250's. Most of them are retired for one reason or another.
There are some common problems they all eventually experience.
If you're able to do minor electronic repairs here are some things for you to look at. If you want more details I'd have to dig out my notes.
One is the memory chip craps out. That's indicated by garbage frequencies showing up. Not being able to write memories etc.
I think I may still have a few memory chips around. I used to remove the chip and install a socket so I could replace them faster. (IIRC they're an ER1400)
Another cause of that can be the regulator transistor. It has no heatsink on it. It eventually burns up. Those I replace with an AN7808 three terminal regulator mounted to the chassis with wires to the board.
The other is the demodulator chip. (I'd have to check to be sure of that)
That chip is no longer available and there are no substitutes for it.
You can pm me if you want more details.
EDIT: I should add the following.
While I really liked the BC-250's, there are a lot of reasons I wouldn't put much effort or $$ into repairing one today.
In fact, the BC-250's were my first 1,000 channel scanners.
A place called 'The Dog House' I think, used to sell a memory upgrade for them. It was just an external switch box with 20 memory chips in it and a rotary switch to select which of those 20 chips you were using.
I bought a few of them. Then, I built external boxes that counted up to 50 then electronically switched to the next chip. A clunky way of doing things but it worked just fine back in the 70's.
1. In two years or so, the FCC regulations will require all agencies to go to a narrower signal. The BC250's won't do well at that.
2. There are a lot of cheap scanners available on eBay, yard sales, etc.
3. Repairing a BC-250 only buys you some time. They're old enough now that it's unlikely they'll run much longer.