The 700C X26 is a rather odd size tire. If you want the tube to be easy to install, buy one that says fits 700C X 23-25 rather than 700C X 28-32. The smaller tube will expand to fit your 26 tire without any problem. I generally buy my tubes from Niagara Cycle where their name brand tubes start at $3.49 but you need to buy a couple to make paying the shipping worth it. You can find the same tubes on eBay for around $5 with shipping included like this one Q-Tubes Value Series Tube with 32mm Presta Valve: 700c x 18-25mm | eBay It's a brand I have used and will continue to buy in the future. BTW I HATE thorn proof tubes. Heavy and hard to work with. If I get a used bike for restoration, it is the first thing I throw away and replace. And yes, I live in tumbleweed and goathead country so thorn resistance is a consideration but I would much rather buy a tough tire than buy a thornproof monstrosity.

When it comes to replacing the tire in the future you will have a much better selection in the 700C by 25 or 28 and it will fit your existing rim.