This is an old thread but I thought I'd mention that I found both missing plastics here:
http://www.pinballspareparts.com.au/03-9017-1.html
http://www.pinballspareparts.com.au/03-9017-2.html
With shipping to the US and converting from AUD to USD the cost comes to about $24.
Or you could buy the complete set (10 plastics) from pinbits or pinballdecals for $30 plus shipping (approx. $8).