There is a very low temp solder available for model makers, so you could try contacting them It is generally used for soldering white metal die cast model locomotive construction kits. It is real solder but just has a low melting point but is a good electricity conductor. I believe the melting point is around 150F which is a lot lower than conventional lead/tin solder. As well as the solder you need a good acid based (Phosphoric)flux.