We had this last year. Dd started a new school and was supposed to have a tracksuit in black or navy with no logos. She is small for her age and though she was 11 she only needed age 8-9 so I know what you mean! We spent an entire afternoon traipsing from shop to shop and there was nothing (Brighton city centre so most major chains available). Eventually I did find one in ASDA that was plain blue but had a lilac lining in the hood but by then I thought if that's not good enough for the school then tough! They haven't said anything so this year I was pestering ASDA as soon as uniforms came out, but even then I had to make 2 trips and several phone calls as I could only get top first time because they were already flying off the shelves. I've bought the next 2 sizes so I won't have to go through the same trauma next year! I must say ASDA staff were very helpful though so it might be worth asking if there is still anywhere you could get one in blue.
YANBU and neither am I (only my tall skinny dd is 10). I've been looking since the end of last term, tried Woolies, M&S, Debenhams, John Lewis, BHS, Mothercare and more. Even tried the dead expensive local uniform shop but no joy