I know this bloke Ron
who owns an Omega Optics
2" DGM-Narrow Pass Band filter and hasn't used it for ages, like 2 years or so.
If you don't turn one up here I'm pretty confident that he'd be more than happy to lend it to you on an open ended basis until someday when he may want to use it again - and he does have a 1.25" version of the same in case he gets a sudden case of star fever.