I couldn't get as many of these as I wanted either. I emailed Migros before the closing date to ask if they could let me know where there may be some available and they wrote to me after the closing date to say that the numbers available are actually limited by the SBB.

I also enquired at the SBB about whether a companion traveller can use a 54CHF day card as well if you buy it for them with your half tax (re: earlier posting), but was told that both you and your friend would have to have a half-tax card if you each wanted to travel on a 54CHF ticket.

Back to the drawing board...