Thompson & Morgan has Blauhilde. If you are willing to go with another variety of purple pole bean, there are others to choose from:
Burpee has Purple King
Gurney has Purple Pod Pole
Park has Trionfo Violetto

I personally grow variety Purple Peacock, which Burpee used to carry but seem to have dropped it in favor of Purple King. I've been saving seed from year to year and I haven't tried the others yet; I find it hard to imagine a variety more vigorous and productive than Peacock. It grows taller than any trellis I've given it. My only complaint is can take a long time to start producing (last year it was about 90 days), but once it decides to start, its a flood of beans until frost.

n2xjk we also really like the purple peacock beans, but I have not tried other types of purple pole beans. Just like you do, we wondered how can we do better? they grow very well, produce like crazy for a long time and the pods get really big before getting tough. We saved seed, this is now the third generation of saved seeds for us. They are flattish tan color medium size seeds. They are planted and have sprouted this year already. The last batch did great, I guess the seeds self selected for our growing conditions, always a good thing. Now I wish I had saved enough seed to share with more people (shared with some family members only). Will make a point of saving more seed this year.

Thanks guys for your replies. Luck would have it that Thompson & Morgan doesn't sell Blauhilde (in the US), but their $4 for mailing an envelope of seeds is similar to Gourmet's $5.66. :-(

Anyway, a few seeds were left over from last year, so I'll plant them in pots and take cuttings and hopefully at season's end have a good supply of seeds.

Ordered Sand Hill's purple beans: Blue Greasy Grit, Blue Marbut, Red Peanut, Royalty Purple Pod. Will see how they compare.

Happy gardening!