Do you have a punch to produce the exterior dimensions of a poker sized playing card?
and/or a die/punch to produce a rectangle of the dimensions of the border on the back of a poker sized playing card?

Use a tuna can.

This is a bit of a necro, but you could look into a silhouette or a cricut to cut your card.

I use photograph corner rounders at 3mm

That's almost as difficult for alignment as trying to print a card on both sides. It gets interesting when you go from quarter inch tolerance of easy tools down to one thirtysecond of an inch touch for playing cards.

Actually, I have a silhouette and they have a PixScan cutting mat with registration marks built in. Basically take a photo of your card sitting on the mat, open it in the software, then it's got fairly good tools to set your cut lines. I've had very good results cutting multi part stencils that require perfect registration. I haven't used playing cards, but I've found it to be good to within a few microns with thick mylar sheet - no visible gaps or overlap on the stenciling. Of course, if you don't already have a machine like that, I second @holdingoutflat's suggestion of photo corner punches. I've found good corner radius punches at craft stores in the scrapbooking areas with 50% off coupons. Much cheaper than a new vinyl cutter.

Vince

Oh I found an ATC die by sizzix poker size. It's called ATC with corners.