The best replacement for borate is borax.

The best alternatives to borate are rated as following:
★★★★★  borax
★★★★  boron
★★★  boric acid
★★★  acq
★  sodium carbonate
★  sodium tetraborate

Your alternative for borate is not listed? Suggest!
Speaking about borate, one probably shouldn't forget about polyvinyl alcohol.

Other search terms related to borate and their ratings are:
★★★★★ polyvinyl alcohol
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borate
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