The NARGS site lists it. I have never ordered from them but have seen it mentioned several times on Gardenweb. It's a seed exchange. If I understand correctly, you pay a membership cost ($12?) and then pick 25 packs of seed from a very long list. You can also donate seeds. Donors get more seed packs. It should be a good way to get unusual seeds. If 25 packs is too many, maybe you can find someone to split it with. I might, if you can get more than one pack of the p. murrayanus. I think they probably run out of stuff. You may want to do a little searching on Gardenweb to see if it's a reliable place to order from.

Also Pineridge Gardens in Arkansas lists Penstemon murrayanus PLANTS for sale but they're out. http://pineridgegardens.com/

Sounds like a great plant that hummingbirds would like. Good luck!

Here is a link that might be useful: NARGS

Here's what came up when I searched for NARGS on Gardenweb.

Here is a link that might be useful: Gardenweb Search - NARGS

Christie, I'm sorry it took me so long to get back to you. Thanks for the NARGS lead. I'll have to think about whether I should join and maybe get access to seeds. It's a little late this season, but maybe I should think about it later in the fall or into winter and see. It's actually a request on behalf of someone else. Penstemon murrayanus likes acid soil, apparently, so I don't think it would do well for me. I'm thinking that Penstemon triflorus might be a better choice for my growing conditions, and it is also attractive to hummingbirds. I think both would tolerate heat and cold, unlike some penstemons, that like cool mountain conditions.

Yes - kinda late for this summer. I think I saw somewhere that their list comes out in December and you might have to be quick to get some of the unusual seeds.

Pine Ridge lost a lot of seedlings this year, because of the freeze. You might contact them, because the lady who runs it doesn't update it very often. She had some that were listed as sold out, when I went in late April. It turned out that she had 1 or 2 of some of those.
I haven't seen any of this species in the wild. They are probably fairly rare.

If you haven't got your hands on some seed already you can buy some from Alplains.

Paul