This is a bugbear of mine too. Very few races have anything other than medium and large/x large and as a 5ft2" lady-person they always drown me. I'm involved in our town's 10k and we did offer small, medium and large but even so, small is too big to use for running in so does as a training top to be whipped off before and after races or to wear to physio appointments.

Apparently these tshirt manufacturers only offer adults and childrens sizes and it's generally thought that women can get away with small adult sizes (!)

My running club also offer tshirts to buy, also in sm, med and large but I've discovered that a childrens age 11 is a perfect fit for most of our lady runners. I'm going to push for some of these 'small' sizes to be printed up for next years 10k because there has to be a percentage like us, who want to wear something that actually fits!

I was in the queue fot finishers Tee shirts last week at the Burton 10 mile and a few were coming back as too small, so when i got to the front I asked for a medium as opposed to my usual small and it fits perfectly.