The melting point for tungsten is 6192*F, you cannot pour them like a regular jig.
Tungsten jigs are made 2 ways. The most common is to mix tungsten powder with glue and mold it, this will not give you as nearly dense/heavy of a jig as pure tungsten.
The second way they're made is by a process called sintering. Tungsten powder is mixed with alloy metals with lower melting points, then pressed into a mold and heated under pressure. This process is very expensive and is where the better tungsten products come from.
The hooks aren't molded into the sintered jigs, the head is drilled and the hook is soldered in. Your better tungsten jigs won't have a hook eye, they'll have a hole drilled through the top of the head and out the bottom. The line is pushed through the hole and tied to the jig hook..
There are places on the web to buy unpainted tungsten heads for about $2.50 each, but most of these are the glue and powder heads.