Hi Lionel,
Just looked at the instructions, they're 3 x 48.5mm. (item number 9805681)
Might be worth contacting Time Tunnels as they have them listed for £3.79 -->
http://goldstarstockists.net/live/ca...efbd87e02ef15f
Fusion Hobbies £3.99 -->
http://www.fusionhobbies.com/Tamiya-.../ta9805681.htm
Or if the above shops don't have any in stock, an Singapore Ebay seller has some -->
http://cgi.ebay.co.uk/Tamiya-TRF501X...item1e5c70e33c
See you at the end of the month,
Nige