Most Japanese companies will NOT supply replacement or spare parts outside of japan, unless they got a local office like Tamiya.
HLJ might be able to help in getting a spare canopy. I know that they do at times order replacement parts, but not sure of their policies for doing so.
If I got paint seepage/overspray on a canopy I use a toothpick to scrap it off. You can also use a cotton-bud/microbrush soaked in a teenie bit of thinner to assists with the cleanup, keep soft tissues handy.
If you need to sand clear parts invest in a top compound or similar.
Either way I don't know near with anything really abrasive, I rather strip the part and repaint it.
Others might have some more suggestions. Best of luck for getting it sorted out.