I'm assuming that the PO cannot be contacted to see if he has those parts...?
Also, have you looked at Thetford's website to see if they have a set of them? IIRC their site is quite complete with regards to replacement parts.
I can imagine your surprise and shock when you discovered that they were missing!
[Edit: I looked at the Thetford site] Attached is the instruction sheet for installing your sprayer,and other than one clamp, I don't see anything else that could be missing. Are you perhaps referring to clamps that connect the spray handle?
That part is not shown at all, which makes me wonder if there are any parts to assemble in the handle part.
These sprayers are something that often gets overlooked when winterizing, i.e. they don't always get effectively drained. Could something be damaged?