Can anyone recommend suitable shocks for a 1976 DT250?  What length should they be pin to pin? Thanks.

My 1975 Dt250B has new springs from YSS. You can see a picture here: ibb.co/MGwVWRH
I can measure them for you.

So here you can find some photos of the rear shocks. Length from center of the pins is 320 mm

ibb.co/Bg7vBzy
ibb.co/M53fhgH

What model of YSS shock did you buy? I see it's the model RE302-320T So the basic model is RE302 with a 320mm length. But looking on YSS's website I see there's usually a full number like RE320-320T-xx-88 and I'm not sure what the xx values represent from their site. I didn't see any DT250s twin shock models listed. Wading through the options I saw a RE302-32T-08-88 which was meant for a 77-80 Yamaha XS 250 street bike which would be kinda close in weight. Most of the others I saw were for much larger/heavier bikes.

Would you have any weblinks for where you bought them?

I'm thinking to buy some aftermarket shocks and keep my originals in a box.

Thanks for the length info.

Those YSS shocks do look good with the black springs. (I use a YSS shock on my modern dirt bike (Honda CRF300L) and the quality is excellent.)
Anyway, for the old DT250 I've now gone for some generic units delivered by an eBay trader here in the UK and they seem to look and work just fine for what I need. I went for 327mm (I think the originals are 325mm)