i have an on-demand hot water heater whose output terminates in a 1/2"
copper female thread.

i need to connect this to 1/2" cpvc pipe (schedule 80) grey IPS-sized
(ips = iron pipe size, cts = copper tube size)

simply screwing cpvc into the copper causes leaks due to the thermal
material mismatch and heat cycling.

i located some guides on cpvc usage and they indicated that i wanted
to use a 'transition adapter" which is comolded plastic and metal.

(see for example http://www.ppfahome.org/pdf/cpvc_manual.pdf )

i found this type of adapter in 1/2" cpvc but it is the wrong size
'half inch' -- it is for cts sized plastic pipe whereas i have ips
sized pipe.

here is the link to the right type of transition adapter albeit wrong plastic size:

http://www.kbico.com/products/union.htm#CPVC%20Transition%20Fittings

i am looking for a source of the correct sized transition adapters
that i can buy preferrably online but phone would be ok too in the
united states willing to sell a small quantity (prefer 5, not a whole
case, etc.) and willing to ship to california.

Hi, I know you want a brass/cpvc molded piece and that does seem to be
recommended, but I found this reference to an all cpvc fitting
suitable for high temperatures and thought I'd pass on the link, just
in case it'll serve you:

http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=CPVC+Fittings&product%5Fid=NSF+Approved+Hi%2DTemperature+CPVC+Fittings

Plastic.com is a good site for lots of less common fittings...though
it doesn't have the exact one you mention. I may search a few more
minutes and see if I find something, but this may be all I come up
with. Good luck from here!
lmnop-ga