Many sugar candy recipes ask for corn syrup to add polymerization to the final candy and prevent crystallization. Body sugaring recipes call for lemon juice to prevent crystallization and maintain plasticity. When corn syrup is not available, would it work to use lemon juice instead?
Try Glucose syrup, usually (in the UK at least) its sold in tubes in the baking aisle.
Syrup (from plain table sugar) cooked thoroughly with lemon juice (or other acid) will at least partially turn into inverted syrup, which is very crystallization proof (cooked a batch down to IIRC 115°C once and stored it in a container, extremely viscous but stays completely amber clear). This is likely what the recipes suggesting lemon juice are intentionally or unintentionally doing.
I'd look for UK versions of recipes. The U.K. Doesn't use use corn syrup, so you can probably find appropriate substitutes on a per-recipe basis.
Cream of tartar. Use about one gram for every kilo. Add the cream of tartar when the water starts to boil before adding the sugar.