Thanks for all the replies. Dipak’s mention of the Mudrārākṣasa is dated at the 4th century CE at the earliest. The word for cloth he mentions is the same one I was interested in: paṭa.

Joseph pushes it a bit farther back to the first or second century CE, although that’s still a bit later than what I was hoping for.

It may be I'll have to translate it only as 'cloth' and not 'canvas'.