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'.
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