Ar mh’anam mhuise, a Mhíchíl, arsa mise im aigne féin, go bhfuil gathaí Chúipid dulta ionatsa, a bhuachaill.

Well I'm not surprised you're having hard time. I couldn't really think of a natural sentence myself, so I searched 4,000 pages of native Munster writings and only found one example:

D'fhéadfainn a rá go mánla macánta go rabhas dulta isteach i rang níos aoirde an lá a chuir an bainisteoir an chréamaraí go créamaraí Dhún Chaoin mé...

As you said "had/have/has gone", but pretty rare. Most of the time when you say "have gone" you mean "gone away" so you use imithe. This could only be used when you mean gone without "away", like "gone further" e.t.c.

Is é. Bhí Maidhc Dainín ag obair i gcréamaraí Dhún Chaoin i rith na seascaidí, mar tumánaí lioraí.
(Tá t leathan ag "tiománaí" i gcanúint na Mumhan)

I'm doing some lessons on irregular verbs, and I have to admit, I'm stumped for a practice sentence for "dulta." I can't even think of an English example in which you'd use a verbal adjective for "go." In Irish, the few sentences that immediately come to mind would use "imithe." Any thoughts?

Can you say "Tá sé dulta go Doire" (?) (He has gone to Derry)

Redwolf