Three Dot is kind of an obscure British brand.
I've had luck finding their stuff on 6pm.com and amazon. I bought this shirt in black: https://www.amazon.com/dp/B001PS4XNQ/ref=emc_b_5_t (it runs slightly small: I'm a S/XS, and the S is snug) roughly TEN years ago and despite frequent wear and abuse (I wear it nearly every week, machine wash/dry and don't even separate colors), it looks brand new. I've bought 3 more as back-up.