Anyone know where I could get a cargo blind for a TL wagon? Does the blind from an earlier 3rd gen fit the same?

I'm carrying our 8 month old around these days and have realised that any stuff in the back of the wagon is a real hazard in an accident.

Wreckers/out of a vehicle that has one is pretty much your only choice.. Mitsubishi no longer sells them new.
Earlier 3rd gens should fit but will probably be a different colour (they came in grey, black and possibly beige)

Maybe consider a cargo barrier if you think flying objects will be an issue - a cargo blind will do little stopping something with some weight and force behind it.

Large plastic containers with lids do well to hold smaller objects and stop them from flying around in an accident.
But anything in the cargo area that could be a flying danger in a crash should be removed really, or placed hard up against the seat back.
Loose objects like tools are a definite danger, but there is lots of storage space with the spare tyre if you must carry bits like that.