Looking for alternate pants with 'snaps' around calf and/or shin area
For next to nothing you can install snaps on any pair of pants you want:



There are kits with anvils and presses and others with plier-type setting tools. Both work well and both are cheap. I'd suggest trying it out on a similar piece of material so that you can get a feel for how they work.

Here is a link for a cheap kit ($4.92 USD!)

If you're looking for more adjustability, you can sew velcro right into the cuff of your pants as well. (And while you're at it, you can buy reflective piping and reflective ribbon to increase your visibility.)