No brand, but I knitted (very easy to do) a pair of fingerless mittens that are great for dog walking or anything where you need a grip. Not the best for -0 temps, though.
Maybe you can find someone to knit a pair. Since your temps are so cold, they could be lined with polartec, fleece or similar fabric. Also, you could have mittens made with fingertip end that folds back, so you can clip those leashes on and off. Basically, they are knitted with a horizontal slit and you just slide your fingers out when you need to. Or here's a slightly different version
http://crafts.tutsplus.com/tutorials/how-to-knit-convertible-mittens--craft-17310 Scroll down to see how they work. They can also be made from socks. You could double up a pair for each hand for more warmth. Pretty easy DIY. Just Google for ideas.
I know they make technical gear gloves with fold back fingertips, so you might try some of the outdoor gear shops.
Or you could try modifying a pair of fingered gloves (or mittens) by cutting a slit (but don't cut off completely) on the inside of the glove where the first joint of your thumb, first and second finger are. I wouldn't slice all the fingers (unless it's a mitten), since you only need those two fingers and thumb to do most things. And maybe you only need that feature on one glove. If you're not handy with sewing, enlist someone and have them bind the cut edges with a zigzag, blanket stitch, some soft binding, or other method, depending on whether they are fabric or knitted.
You can get ideas of what I mean from looking at what's for sale online.