Hunt around on line, and then call around. Try:

IPSracing.com
Modacar.com
randdmotorsports.com
inlinefour.com
optauto.com
jdmhondaparts.com
kingmotorsports.com

and I'm sure a bunch of others, just shop it around, you'll find a deal.

On a side note, with those cams, not only do you need the retainers, but you also need the valve springs, or at the very least, the port flow inner valvesprings...

Later,
Aj