I would suggest one of the wide range of Linear Tech current mode
controllers. Get one rated at least 36V (a little headroom helps).
Go to
http://www.linear.com/
select Power Management -> Switching regulators -> Stepdown regulators
At the next page select (from the drop down box)'High Input Voltage' ,
then 'View category'
At the next page, select 'View table'
You'll see a whole list of devices that would suit your needs for Vin
and Iout. Monolithic means the switch is internal (so all you need to
provide is the external schottkys, caps and a small inductor) [I'm not
trying to teach you basics, just trying to be complete]
There are a number of devices there that should meet your needs, *and*
happen to be easily available from your favourite mail order parts
company.
Cheers
PeteS