Joe Breeze HiteRite altenative... ideas before I get hacking! I think the old HiteRite seat dropper springs are excellent for cost and simplicity, but of course they are like hen's teeth now. 
I've been looking at torsion spring suppliers and adapting seat clamps and collars to make one (actually a few, as I have some pre-orders :) but JUST before I get hacking, does anyone know of an alternative that's still in production, or a common hack/mod to make one? 

Added as requested: here's an advert for one where you'll see what it looks like and how it works:



Cheers!
Ben
Many people do seat posts that  achieve this - have a search on google for "Dropper seat post", All of the current models are almost certainly more reliable and easier to use than a simple spring, and can be activated while riding. The fact you cannot find any like the HiteRite is probably the effect of what we now refer to as Darwinism - not bad in it's time, but things have moved on since 1984.