I purchased a 28-300 Tamron lens some years ago and after 18 months it stopped automatic focusing. Tamron quoted me $100 to repair. I chose not to have it repaired and since have only purchased Canon "L" lenses for my Canon bodies.
Welcome to the forum! Beautiful pictures...I particularly like the spontaneous portrait of the two young women. I also like your watermark, it is there but not overwhelming. Thank you for sharing.
Place an ad in CraigsList, or similar community publication, asking for some kind soul to donate one for your photographic mission...who knows what you might come up with (a Gitzo?).
Welcome aboard shipmate. I too went the way of building 1500 in Pensacola, Florida (Navy Photo School) but a few years before you. Looking forward to seeing your work...and exchanging "sea stories!"