Oh No Becky! I can understand exactly how you feel. It is a horrible feeling in the pit of your stomach when something like that happens.
Let me try and give you just a little hope that you shouldn't give up just yet.
A couple of months ago I somehow managed to lose one of my (very expensive) diamond earrings that my husband gave me as a very special gift after baby #2 was born. This was the most special gift he'd ever given me of and I was very, very upset. I also knew how sad he would be to find out I'd lost it. I kept looking and looking and after a month gave up. I told him after a couple of weeks and his reaction was what I expected - very sad (although he understood that these things happen) which made me feel even worse. ;-(
Then...... a couple of weeks ago (we are talking three or so months later), I looked down casually at the floor (contemplating what shoes to wear with my outfit) and nestled in a crazy spot in the carpet pile was a teeny-tiny little twinkle. I knelt down looked down and there it was! (I was flabbergasted - I found it in a different room I thought I lost it- doh!) I was so happy, I literally cried.
Now for you - you've checked the tomato patch very thoroughly, have you checked places like the compost/green waste bin or even the rubbish bin if you have done some pruning? What about if you have a basket you put tools away in - have you checked in there? Have you checked inside gardening gloves? What about the basket/container you may have collected tomatoes in? I'd be sure to check the laundry/bathroom where you were washing your hands as well. Check your gardening clothes in case it fell into your pocket or something like that.
Finally, Becky please don't give up hope just yet, it really may still turn up. I will cross my fingers for you that you have the same good fortune (although with a lot less waiting)!