Try here:
www.aliexpress.com and search for D-BH109. Alliexpress is a broker for Chinese merchants. I think you can probably find them less expensively on eBay, but I was happy with my transaction. I have not seen a genuine Pentax copy, but I would guess that this unit came off the same manufacturing line, but without the Pentax logo. It seems well built and fits well. The pictures on the site are as good as any I would likely post here.
I have two, both packed with eneloops. I put a small diameter heavy rubber band (courtesty of my green grocer with a bunch of brocolli) around the spare and put that in a plastic bag. The cells stay put and can't short; at the same time I can swap power packs in seconds without fumbling with individual AA cells in the field.