It is basically normal to see frost on the outside of the regulator. The gas
cylinder is full of dry ice, at the 800 psi or so that it is pressurized to; CO2
gas comes out as the dry ice sublimes from solid to gaseous phase. So, it is
normally pretty cold coming out. Also, by the physics of the "PV equals NRT"
equation, as pressure drops, volume more or less constant, temp will go down.
The only time this is a problem rather than a simple nuisance is when there is
enough water in the CO2 to freeze up the inside of your regulator. The water
results from the tank having recently been hydro tested (pressurized with water
to test its ability to withstand the pressure; periodic requirement, see the
dates stamped up at the top of the bottle), and not properly dried out before
being filled and delivered. Even commercial grade CO2 should not have enough
water to freeze your regulator, bone dry definitely should not. If this occurs,
you will see your gas flow fizzle out, your flies wake up, and fly away.
Complain to your gas supplier and get a free replacement cylinder.
There are heated regulators, and maybe this is what you need, but I have never
seen them to really be required. My last lab was looking for them through the
normal lab suppliers, but had no luck; a specialty gas equipment distributor may
be your best bet. They (my old lab) lost interest in the quest for a heated
regulator when we got the wet tank replaced and the problem never reoccurred.