I would suggest an anthology or two or three --
An Leabhar Mòr is absolutely wonderful (with splendid illustrations) drawing on a panoply of Gaelic poetry from across the centuries from Ireland and Scotland (recognizing the shared Gaelic heritage) -- available from The Gaelic Books Council https://www.gaelicbooks.org/product/an-leabhar-mor-the-great-book-of-gaelic (also on Amazon but more expensive)
Nua-Bhàrdachd Ghàidhlig is a relatively inexpensive selection (under $15) of modern Gaelic poetry that would give you a good start -- found at https://www.bookfinder.com/search/?full=on&ac=sl&st=sl&ref=bf_s2_a1_t1_1&qi=,3GPty1Jdo77XERPJnl16Cb6Rc4_1497963026_1:2:1
An Tuil edited by Ronald Black is a great reference source (400 pages) but it's out of print and if you can find it pretty expensive. (Why Gaelic publishers haven't discovered the digital world for their books, I can't tell you.) Bookfinders lists three sources for more than $100 https://www.bookfinder.com/search/?ac=sl&st=sl&ref=bf_s2_a9_t1_18&qi=ECZBNnfnBj59WhQ10SiCaJmG0oU_1497963026_1:24:15&bq=author%3Dronald%2520black%26title%3Dtuil%2520%2D%2520the%2520flood%2520anthology%2520of%252020th%2Dcentury%2520scottish%2520gaelic%2520verse
For historical poetry -- you might try
Duanaire Na Sracaire: Anthology of Medieval Gaelic Poetr*y For *$1.99** on Kindle, you can't go wrong https://www.amazon.com/Duanaire-Na-Sracaire-Anthology-Medieval-ebook/dp/B08ZSN4SK9/ref=sr_1_8?crid=20GSSJTGB1UXF&keywords=gaelic+poetry&qid=1646517948&sprefix=gaelic+poetry%2Caps%2C133&sr=8-8
An Lasair (The Flame): An Anthology of Eighteenth-century Gaelic Verse -- available on Amazon for more than $30.
If you're interested in random assortment of contemporary Gaelic poets, let me know, I could provide list.
As well, if you'd like free (!) public domain poetry (from 1900 and earlier), likewise, I could provide links.