Amazon's just the platform, these are sold by a third party vendor hence the comically jacked-up price. And they're not even OEM parts. ("Plytx" / Playtex Replacement)
Have you checked if Amazon.com has them listed? For certain niche items it sometimes makes more sense to order from there (even with shipping+duties) instead of Amazon.ca. Food for thought.
Edit: Are these right?
US$18.94 + US$9.65 shipping, no duties.
So yeah... Unless you call the manufacturer and beg for parts, might be best to just get new cups sadly.
Edit 2: Well.ca used to have them for C$5.96 but are listed as "discontinued", which may explain your challenges finding them.