The front-panel tactile push buttons on my TS-140 became intermittent and unreliable. I searched for the Kenwood part number S50-1412-05 but did not find any sources. I did find an exact match for an equivalent part on DigiKey. The DigiKey part number is 679-2428-ND. The manufacturers part number is MJTP1230. The price is USD 0.10 each.
I replaced all 10 switches on the front panel and they work great.
It is an effort to dismantle the front panel assembly to remove the board holding the switches. Go slow and take pictures at each step before dismantling. Don't just pull on the flat-cable connectors; there is a release bar at the top of the connector which secures the cable and provides a low insertion force when reinserting the cable.
When you do a search using a Kenwood part number they will be the only supplier. You have to figure out who the supplier to Kenwood is. As you did. At least you found a sub.