Are the rims still good [MENTION=569237]RootbeerRaleigh[/MENTION] ? If the rims are good and relatively rust free, then you could replace the nipples. Most nipples are brass, but I think Raleigh used to make steel ones. Could someone confirm or deny that?

For me, and keep in mind my values and resources may be different from yours, I would first replace the nipples if that was the problem. If it is the rim, I would replace the rim. Yes, it is true, my favorited CR18 rim seems to be unavailable in the 26" x 1-3/8" size now. Rims are hard to find in this size nowadays. You may need a 32 hole rim and 40 hole rim for your bike. If you are getting new rims, you will have to check this.

Lot of members here like to site the relative lack of abundance of tire in both 26" x 1-3/8" and 27" x 1-1/4" size as a reason for switching wheel sizes. But as long as you can find a tire that meets your needs and budget, you are set.

I happen to like the 26" x 1-3/8" tire size and see no reason to switch on a bike that already has that size. If you cannot source the rims in the US, and I know it may be hard, other countries did not abandon the size. Particularly Japan, Holland and the UK. You can try SJS Cycles if all US sources come up empty;. SJS Cycles 590 rims

Tires are easier to find the US. I have Schwalbe Delta Cruisers. They seem to be available in the US and there are other choices as others have pointed out.