Found good source for hyd quick release caps

[Tibbits]

These are the caps for both ends of a 3/8" quick release couplers. $10 total for 8 male and 8 female, plus $7 shipping. The site has many sizes. The quality seems OK, but they are all red. Seemed the best deal I could find.

CZB-3/8 ISO B Cap
8 $0.56 $4.48

PZB-3/8 ISO B Plug
8 $0.69 $5.52

Got them at:

Hose and Fitting Supply