Really depends on what type you want!!
Do you want up and over,roller,open out,panel,wood,electric?
Do you want it delivered and installed,or collect and fit yourself!
Have a good google for garage doors,you will find 14000+ hits for them!
B&Q, Marley Hormann,Cardale,Glideroll,etc!!
Ebay was where I found my new unused one at a cracking bargain price! :wink:
Fitted it myself in less than a day!!