I am from the English Midlands and say Mom. I get really annoyed too when trying to find a birthday card or gift for my Mom with Mom written on it and can never find one. They're invariably written in the southern English Mum style.
I guess you'll have to send away to America for them or make your own.
To Re Jim,
Well spotted: "grandpa" not "granpa". I never use it anyway.
Make your own, you've got a computer right?
HellifIknow, I say Mom. I have only been to the UK twice so...
I noticed that some of them say mam or what not but grandpa/granpa water/wa'er I never considered mom/mam etc. as a major differance.
I use "Grandad" and "Pop" (depending on which grandfather I'm talking about) or "grandfather" (for both especially if I'm talking to someone who doesn't know the distinction I'm making between "Grandad" and "Pop").
... I guess that should be "Granddad" not "Grandad".