Thanks for the advice all. The moulds I have are rubber blocks for pour casting. Very low tech i.e. my level!
In the olden days, when Steph was but a lad, he had a kit for building toy soldiers, cannons etc from a company called, I seem to remember, "Prince August" who had a factory in Macroom, ROI. In fact (I must be getting the hang of this computer thing) they are still there - see
http://www.princeaugust.ie/
Their web site gives pretty good instructions about using the rubber moulds and is a potential source of the white metal for low temperature casting although I suspect that it might be a bit pricey but possibly worth a shot.
However, the reason for this message is to say that the quality of the castings produced from this set up was surprisingly good, details were good and crisp and one could cast quite fine items, like the cannon wheels, for example. In your position I might just try the lo-tech approach to start with. I know that the Alex Tiranti stuff has a good reputation but the capital outlay may be a bit eye watering.
Of course, we cast loads and loads of soldiers and cannons, because that was the fun bit. Most were never painted though. I remember 'er indoors used to cluck round us, and in retrospect quite rightly, as seven or eight year old boys and liquid metal are not a terribly good combination. In fact, of course, the toy soldiers were really to keep dad happy - rather like Steph's first model railway, and look where that's got us!
Just as a side comment. I and many others like me hve a box of white metal scrap which is a useful source of castable weight for locos, but the rate of accumulation exceeds the rate of usage. I could make a few kilos of this available to you, FOC of course, if we met up at an exhibition (Kettering for example). A few kilos is not much volume, of course, but might be helpful for test castings at least. However, a word of caution - I don't know whether the white metal used for casting in rubber moulds is of a special grade which maybe melts at a low temperature. You'll probably need a metallurgist to tell you that.
Best regards.
Brian