I think I would like to have a go at it, assuming the southern US is a suitable climate. Any specific recommendations for a good source of seeds?

Why not grow mimosa? If your in the southern U.S. you are near enough to Mexico where mimosa hostilis grows naturally it is very feasible to grow outdoors directly in the ground.

I have grown rather small Acacia confusa plants. They love the summer sun, and generally grow very quickly if given good soil and rhizobium bacteria. Acacias are legumes, so they will fix nitrogen.

You can try to bonsai one and keep it inside in a largeish container. Any frost in the ground would likely kill it.

I've been meaning to test my collected phyllodes & stems in an aya analog brew, I suspect they are active but not so much as the bark. Also good to note lots of different factors have been known to change alkaloid concentration in the Acacia genus.

I'm sure you can find a seed supplier in the Sustainable plant and seed suppliers subforum or google. The trees are abundant on Hawaii I'm told.

I live in USDA zone 8, and it looks like neither mimosa nor acacia can survive in any zone colder than zone 9. So, I guess I'll look into plants than can survive better in this climate. Maybe I'll try to bonsai one as was suggested. Im sure mimosa would be fine probably 10 months out of the year, but Jan and Feb here can get very cold during the night.