i struggled to find a complete one small enough for my 6 yr old tiny niece so i have just been collecting random brushes as i go and bought her a pink oyster bag to keep her brushes, gloves, treats etc in.
so for quite a while she was grooming my pony with a face brush until i could find a small enough body brush!!
Countrywide had some for about £15 for a complete set. They were either pink or blue and came in a matching box. Not sure if all of them had straps on.
I have really struggled to find anything that has everything you'd need. Thy usually have a small body brush, small dandy brush, small plastic curry, hoofpick and a sponge. Which IMO is pretty rubbish.
Do you have a derby house nearby? or are you near to robinsons? I know both sell small stuff individually as well as in sets, so perhaps you could get a pink bucket and put it all in there?