It's just an 8-speed triple front derailleur, nothing special.

You can replace it with any other 8 or 9-speed road triple front derailleur. I take it that it has a band clamp built onto it, since you wrote that it's a 28.6.

So any 8 or 9-speed front triple derailleur with a 26.8 band clamp OR any braze-on triple front derailleur, AND a braze-on clamp adapter with a clamp of 28.6 will work.

I've been pretty happy with the used braze-on Shimano 105 FD 5504 9-speed front derailleur that I bolted onto my Trek 1100 when I converted it to 8-speeds last year. I think I paid like $2, plus shipping (about $10) from a eBay Seller. I put it on a braze-on clamp adapter. The braze-on clamp adapters come in different sizes, so if you buy an adapter, make sure that it's the right size to fit your bike's seat tube (28.6).

I bought the braze-on clamp adapter new, from a eBay Seller for about $7, including shipping (about $15 from the LBS). Later I got wise, and bought a couple of used Shimano RX-100 braze-on derailleurs for $2-$5 each, that came complete with braze-on clamp adapters (that are the correct size to fit my bikes). If you look on eBay, you can find good used front derailleurs complete with the braze-on clamp adapters for less than I paid for the new braze-on clamp adapters alone.

There's a Claris 8-speed front derailleur sitting here that I took off a Felt F-90 that I parted out. I'm not crazy about it, because it has a stamped steel clamp (marks up the seat tube). For that reason, I would not recommend the Claris front derailleur. It's in good used condition, but the clamp is 31.8, otherwise I would have offered to you.