You can find them on Premier1 website.  MUCH safer than standard glass lamps, and last MUCH longer

I am no longer raising chicks.  My lamp I sold to my neighbor.  But I have these replacement bulbs.

They are $30 new (for the 600) and $35 (for the 1200

So a good deal.

If you raise chicks, buy the lamp, and then get these as replacements, on the cheap.