I've managed to lose the front cap to my Sony VCL-EX0877 wide adapter.
:~(
Anyone know where to find a replacement?

Try this link:

https://servicesplus.us.sony.biz/sony-parts.aspx

Thanks for the link Jim,
I'd spent an hour blundering around on the internets and knew someone here had the answer.

A painfully expensive lesson in "where's my stuff"

No problem. Rusty. I recall losing a lens cap for one of my previous cameras (might have been the PD-150) and ordering a replacement from Sony.