I have just recently bought some fake cockatiel eggs for the same reason as you. I also only found them in the US via Ebay. I think it was called something like 'The Egg Shop'. They were delivered really quickly though and are very realistic looking. Sods Law though and my cockatiel pair seem to have stopped laying eggs for this year just as the fake eggs arrived so I haven't had chance to try them out but at least I have them on hand should they lay again next year.