I've spent the last few minutes looking at the material safety data sheets (MSDSs), and it appears to vary by manufacturer/supplier, but most seem to use toluidine dissolved in either acetone or another hydrocarbon solvent.
Water does accelerate the curing process for cyanoacrylates, but I don't think this is one of those situations where more is better... In other words, don't apply too much water.
As to trying to pick this stuff up in London, just a warning that CA accelerator isn't supposed to be shipped by air.
By the way, lacquer thinner ought to be available in Poland, assuming there aren't any legal restrictions which limit it's availability since it is a mixture of acetone, xylenes and other chemicals. Here in the US it's usually found in hardware stores with the other solvents such as paint thinner, acetone, turpentine, etc., but I would also try automotive stores (car paints are usually lacquers). Some art stores have it too. As a last resort, you could try asking a shop that repaints cars if they could give or sell you a small amount. Be forewarned that it can melt polystyrene, which most kits are made out of.
I can do all I need to do with paint thinner, which is a bit gentler, so that's all I use.