My father-in-law has 2 identical gas grills; here's one of them:
While using them over Thanksgiving I discovered that the thermometers are no longer accurate and I'd like to send him some new ones, but need to know what model they're for. Thanks!
That looks like either a Genesis or a Spirit. The thermometers used in those are the same for all the older gas grills and can be found at Home Depot. Here's a link to it on one of the online Weber parts stores.
Looks like my silver B,, fold down table on the left and 3 burners. The only difference is that mine has an enclosed bottom with doors. You couldn't pry it out of my paws, great unit.