Hi T,
Sorry to hear of your woes.I know how it is with such misplacements and the joy when you find it later, having just purchased another.
Anyway, if I were you I'd start here - Go to the table at the bottom and use it to find and short list all the other Canon 18.0MP APS-C sensors (EDIT: you can
probably limit that to all those that use the similar DIGIC 4 sensor, also listed there)
https://en.wikipedia.org/wiki/Canon_EOS_1200D
AND then ring Canon Spare parts or 3rd party parts and tell them you are a repairer and that you'd like to buy a sensor and ask for price & availability
and Part number of your sensor and then to not make it so obvious call about the other few 18.0 APS-C sensors you identify or see how you go - ASK all at once, you never know. Then off to ebay or Gumtree to find your sensor.
OR better yet, keep looking and ask for the intercession of St Anthony of Padua, the Patron Saint of lost things ....
Best
JA