Not really specifically for bikes obviously but I've seen several people have good luck using these phone screen protectors on bike frames.
$1.25 for 5x3.5 sheet and free ship
Cut-to-Fit Screen Protectors and Screen Covers | XtremeGuard
Mtbr's 2016 Winter Biking GearReviews and Roundups
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Thread: Cheap "Frame Protection Sheets"