Air gun O-ring?

I've been trying to find an o-ring kit that I can buy that would give me a good selection of O-rings to do maintenance on my guns.
The SAE and the Metric kits I got from Amazon doesn't have any O-rings that I can use. They are all the wrong sizes.

My question is:
Does anyone know of a useful kit that I can buy? Or a good source for O-rings sizes that they use on our air rifles. (FX in particular.)

Any help would be greatly appreciated!
 
Here is another one, but does not have urethane o-rings: http://www.oringsandmore.com/

Some urethane sizes are available at McMaster.


This ^^^. Most likely the o-ring you are looking for is metric. Mcmaster sells every conceivable size, even in half-mm sizes. Viton-based o-rings are a good universal compound to get as well, as they withstand a variety of compounds (except acetone or KEP). I am not familiar with what size you need, but if you figure it out, I might have them on-hand as well.