Does anyone have some tips for getting larger light fixtures like the ones in the title?

I've always found it really difficult and a little expensive. When I got my troffers (brand new) online, it took a lot of searching and the shipping was a lot. I've also always wanted some louvers, but they seem even harder to find online.

Keep an eye on renovations and demolitions. If you can talk to the site foreman and be ready to offer cash, you might get pleasantly surprised. That is how I got my louvred fixtures.

Troffers are easier, you can probably still find them a lot on sites like FB Marketplace. Renovations and demolitions are a good source too as are change outs.

As for louvers those are harder to find. Sometimes you might also seen them on FB Marketplace as well.