Chris,
I don't know if they are similar enough, but one option, if you don't find a Peggy kit, might perhaps be to convert the Mountfleet Models generic steam drifter Danny Boy?!
From a quick image google I get the impression that the hull shapes might have been a tad too different (from at least osme photos the Peggy seems like she might have had a shorter foredeck?), but perhaps worth looking into anyway?
My main reason for suggesting this, though, is that both Caldercraft and Mountfleet Models were originally Frank Hinchliffe enterprises, and I suspect (on the verge of knowing for sure) that he re-used his own earlier work a lot. As I believe Caldercraft was previous to Mountfleet for him, a lot of what had gone in to the Peggy kit might thus well have turned up again in Danny Boy … ?!
Mattias