Found this place in the states for shocks, might be worth having a look at.
http://www.car-stuff.com/monroeshocks.htm
A friend of mine has bought loads of bits for his mazda's from the states as parts are available over there so work out cheaper.
I have also spotted one monroe gas shock on ebay, not much use on it's own but he did put the part number up, so find a monroe shock dealer and see if they can sort a pair out for you.
Part No. 43054 (Monroe Gas matic)
Doh, I got the wrong end of the stick! Thought you were after stock shocks! (£28.50 each plus £9 carriage from proven-products.co.uk if anyone is interested)
When I last lowered a S12 I secured the rear springs by drilling a couple of holes in the spring seat and cutting a plastic coated coat hanger up and threaded it through the hole, over the spring and twisted it up to keep it in place.