From my own experience Chaetomorpha species tend to be most common around high nutrient areas near bird nesting islands (rookeries) and along inland bays and such. That would be the first place I'd look, Ulva (sea lettuce) would also be very likely there as well.
You could theoretically use any algae for a refugium export species but Ulva, Chaetomorpha, Caulerpa and to a lesser extent (IME) Gracilaria, Enteromorpha, Halimeda, Hypnea, Halymenia and similar can also be used, but grow more slowly.
>Sarah