I was looking all over the place in Sydney and Newcastle for T-MOLDING, couldn't find any anywhere, so I just ordered from t-molding.com in the US.
Great service from them, and what with the exchange rate at the moment the $$'s were not to bad.
5/8" is pretty darn close to 16mm - I am using 16mm MDF for my cab, so it all works out well.
I though about going with a thicker MDF (18mm) but there is no non-metric size T-MOLDING close to 18mm - 3/4" is just over 19mm.
Cheers
Martin