FYI. Most vintage 7-speed rear wheels have 126mm spacing ... so, that's probably true for your bike's rear wheel, too.
If you want to buy a new wheelset, then you will want to respace the frame to 130mm & subsequently realign the rear derailleur hanger. Neither is particularly difficult to do -- the only thing you need to know is that you should NOT use any additional leverage than you can provide with your upper body.
If you hadn't already thought about it, why not simply have a new rim laced onto the rear wheel?
A lot of people recommend the VELOCITY Arrow rims -- I've never used them.
I think that ALEX rims are probably better than most people realize -- they are available in a variety of profiles.
MAVIC rims are ubiquitous ...
I like AMBROSIO rims, but there is apparently only one source in the States unless a person can convince their local Colnago dealer (!?!) to order some Colnago labeled Ambrosio rims.
There are several other brands of rims, but they are no longer readily sourced in the States -- e.g., RIGIDA, to name one brand which I think is still readily available in Europe (at least, it was 10 years ago!?!).
If you aren't going to relace the front wheel, too, then you probably want to choose the rim whose profile most closely matches that of the Araya rim which it will replace.
