Refridgerated is a very pricey shipping option and not something you will find many distributors willing to handle. Fedex does support dry ice shipments but you need to have a sizeable volume to really find anyone willing to put them together for you. If you have a smaller operation you may want to contact FedEx and UPS to see if you can pack and ship yourself.
I have 2 snakes and buy frozen rats from RodentPro.com in bulk.
They ship it UPS ground (I assume if I was in CA they'd ship it via 2nd day air, as it is ground is only 3 or 4 days). They also only ship on Mondays or Tuesdays so the box doesn't end up sitting idle over the weekend.
Their shopping cart is ingenious because it automatically calculates how much room you have left in your refridgerated box, so you can get the most bang for your buck shipping wise.
Anyways, their boxes are thick corrugated matter, maybe two ply, I don't recall. Inside is some fiberglass insulation, the same stuff you'd use in your house, only thinner. There are two pieces, forming a cross and folded over, so the contents end up insulated on all 4 sides. The rats themselves are in plastic bags and packed with dry ice. Normally when the box arrives the ice is not yet fully melted, and the rats are still rock solid, so their system seems to work.
I've also ordered from food places online, they too use dry ice, but they shipped in heavy duty styrofoam coolers/boxes made for shipping.