Need help with Tube size.
 

I have what I believe is a Spin Mtb Trispoke. I found the right tire size which was 26 x 1 1/8. Problem is I cant find the right tube. I've tried two tubes one from Continental which was a Tour 26 (650C) ALL. and one from SHWABLE Sv 13. Both were too big. I looked online but I'm only confusing myself. Any help is appreciated.

Easier to find the metric equivalent versions listed which would be 650 x 28mm wide. You can fudge the width a few millimeters in each direction (23-34 or so) but a little narrower is better than wider.

Consider specialized tubes. You'll be able to find a tube to fit with the right stem for your rim. Just like 700C tubes can be used with 27" wheels, you can use 650B tubes with 26" wheels. Since 650B wheels are intended as smaller road wheels, they're more available in narrow widths.

I find that sourcing the exact size bicycle inner tube that I want to be a frustrating experience.

This winter I changed tires on our recumbent trikes. I wanted erto 406 x 2.0 inner tubes with 40 mm Presta valve stems and erto 559 X 2.0 inner tubes with 40 mm Presta stems. One can burn a lot of gas chasing from LBS to LBS searching for those exact combinations. I can find what I want on the internet but was amazed at the range in prices and shipping times required by some vendors. I can understand settling for a "not exactly" inner tube in a pinch (pun intended), but if I'm buying tubes in February, I want what I want.

You're sure that the Mtb Trispoke wheel takes a 26 x 1 1/8 tire and tube, or are you assuming that the "26 x 1.125" on the tire means the same thing? Mtb tire sizes are almost invariably expressed as decimals:
e.g., 26 x 1.75, 26 x 2.125.

The late Sheldon Brown's intro to tire sizing

From that page:

Brown's Law Of Tire Sizing:

If two tires are marked with sizes that are mathematically equal,
but one is expressed as a decimal and the other as a fraction,
these two tires will not be interchangeable.

Find the ISO/ETRTO or what Crankycrank called the metric size of the tire, It's on there somewhere. Some mfrs. make it reasonably prominent, but others only have it molded in the tiniest of print somewhere on the sidewall. Then look for a tube that both measurements are within. Tubes are generally made to fit tires of various widths. So you have to look for a tube that your tire is within it's range, Though last time I had to look, it did seem like tube makers were trying to further simply things by giving little information about such.

If I couldn't find a tube my tire is within the range specified, then I'd go with a small width tube before bigger width.

Oh.... also some mfrs of use a bastardized form of ISO/ETRTO and will state 700 or 700C instead of the correct BSD number of 622. Don't know if they do that for other sizes such as your 650.

So I actually got some tubes from specialized that Unca_Sam recommended . They were 26 x 1.0 - 1.25. Fits perfectly. Should've mentioned that this mtb rim was going on a track bike. So I was looking for a tire that was narrow enough to fit the fork.

It's better if you learn the metric ETRTO size for next time you need to shop for stuff. I would guess almost every mainstream manufacturer will give metric specifications, because ETRTO is a more precise measurement of compatibility to 1 millimeter. There are 25.4mm in 1 inch. When sizes are given in inches, you won't be able to tell how close that last fraction of an inch is to the next whole inch, unless you know the archaic relationship of the inch width standard to it's diameter.

https://www.schwalbe.com/en/groessenbezeichnung

Tubes are easy to find in Europe. Schwalbe makes them in almost every size and there are giant internet retailers who stock them all, like bike24. And they really do arrive in 1-2 days when you order before 1pm (depending on how far you are located from their warehouse).

I hear you can write messages on small pieces of paper and train pigeons to deliver them, at least until someone develops a way to transmit the human voice over vast distances, but with the price of crude, driving might make more sense... :)