There is reselling to other investors: dnforum.com, namepros.com, domainstate.com plus many of webmaster/IM boards have domain areas (ie. digitalpoint)

Marketplaces: sedo, afternic

and plain ol' contacting people who might be interested via email, phone, letters, walking up to their store.

If they're Australian domains and you have a portfolio you want to offer, you could try Drop.com.au who sometimes do specific auction sales in addition to their daily droplists. I buy there now and then.

how do you get around the Business Name / Trademark rules?

You can lay claim to a .com.au if the domain name is "closely and substantially connected" to you as the registrant. This includes things like selling a product or offering a service with that name.

auDA ruled a few years back that "domain monetisation" falls within "a service that the registrant provides" (with a few exceptions).

Sales/transfers of domains were a bit painful back in the day but have been relaxed now. There are restrictions (from memory, you can't register a domain and then sell it within six months) but it does make speculation a bit easier for domainers.

to other domainers: dnforum.com or sedo.com .

flippa.com