I use airline gift cards all the time. Costco has southwest on sale and they regularly also have Alaska. Target has Delta and Southwest, probably United too.

I believe you can also get a visa gift card, and edit the billing address directly through Visa so you can process it through the airlines website. I haven't done this.

I have purchased flights using my Cash app card, which does not have my legal name associated to it but my address. You can deposit cash onto it, or just have subs pay for it.

I don't think it's smart collecting numerous cards over the course of a couple of months. Just get the $500 card(s) when it's time to book?