Tempered glass is what is used in those windows, a type of safety glass because unlike standard glass, it breaks or shatters into small less harmful shards. It can only be cut to fit before it is tempered and then can be sent out for tempering.
It is possible that your window may still be considered a standard RV window size and can purchase the rubber seal and tempered glass as well. There is a very good RV window maker in Vancouver, Wa. which you may be able to do a search and find. It's funny how they sell to the outside public easily enough, but when you call an RV dealer to find them is like proprietary information and will instead get it for you after they mark it up. I don't mind the mark up really so much, but the possibility of size mistake or getting lost, taking longer with the dealers hands on it.
I'm sorry I did not keep their name at least.... they were very high quality people to deal with and actually used their RV windows for their office windows.
An interesting side note that I found most glass shops either reluctant to reveal or didn't know so they can handle it, do their mark up etc.,is that oven glass is not tempered glass and nor is woodstove glass a tempered glass. It is what is called ceramic glass and can be cut to size while you wait. And this RV window maker in Vancouver has Ceramic glass in stock. They were honest people and know their trade.
Sorry to get off topic about ceramic glass.... I mention it because this really good rv window manufacturer keeps it in stock which many places do not so it is possible this information can be used as a search tool to help you find them in Vancouver Wash.