How about Fimo clay (or possibly Sculpey clay in the US ?)
Coloured modelling clay like plasticene but you can harden it in the oven.
Otherwise Wizards of the Coast have some snakes in their D&D miniatures range, but mostly giant ones.
The latest D&D range (Deserts of Desolation ?) has some quite good swarms of scarab beetles etc that are quite useful, maybe they'll do swarms of snakes in the next set.