I'm using the one from the collection on IAMPETH's site. It's labeled 'Ornamental Penmanship Capitals by H.P. Behrensmeyer.' Do you know where I could find other collections?
Ah yes, I know that alphabet. I've been lucky enough to seem some Henry Behrensmeyer originals, and his work is distinguished by an exceptionally light, delicate touch. He used a version of that type of P for his signature on the cover of "Lessons in Practical Penmanship", by the way (see below).
I don't know where you might find a collection of Behrensmeyer's work, although there are some nice examples in Blosers "Lessons in Ornamental Penmanship", but there's a fine selection of capitals from plain to ornate in the "New Spencerian Compendium" plates 19-24. The Madarasz book and Jones' "95 Lessons" are other good sources, as is Zaner's OP book which contains a few upper case alphabets by Lupfer.