My experience is that pre-oilers are a rarity on GA aircraft... More
seen on high end yachts, exotic race motors, large commercial engines
on cargo ships, engine tinkerers, etc...

The real issue is do you need one? If you fly the airplane on a weekly
basis, then the parts will still be oily and oil pressure will come up
quickly upon starting..

--- BTW, your oil pressure gauge is not a good indicator of how fast
the oil galleys start flowing oil when you start the engine... I could
rattle on for paragraphs (as usual) on this, but just be aware that it
is slow to register pressure with cold oil for several reasons ---

If the airplane sits for weeks at times, then you need to look at the
pre-oil issues... Actually, the suggestion of using compressed air to
splatter oil up on the cam, rods, cylinders, is a workable solution...
It is the cam/lifter that suffers the most from dry starts - not that
being dry is good for pistons, mains, etc...
The biggest barrier to a pre-oiler in GA aircraft is weight, cost, and
certification issues... Actually, as I am typing this a workable idea
came to me that would be portable device and not require an STC...
Probably a market out there for a device that is under $200... I'm up
to my eyeballs in starting another business right now (and my wife is
ready to choke me) so I don't have the time or energy to follow this
up...

The reality is that rust is the crime against an engine... Training
fleet engines that run every day routinely go beyond TBOH... As do
pipeline patrol airplanes, cancelled check haulers, etc..

denny