I get the same behavior, it only allows 10 GbE SFP+ SR transceivers, but it allows more of the other 10 GbE SFP+ transceivers. It does allow me to type in 32 on the 10 GbE SFP+ SR transceiver line, just not use the arrows.
I didn't try submitting it with the typed in 32, so I don't know if form validation will stop it. If you submit the form should end up with a sales rep, so you can have them adjust it as needed before you order. Also, off brand optics work fine, so any pricing you find on the Internet for the optics is probably better.