Completely unrelated to your original question, I recently got a pack of gas struts for another project that I made for someone, and now that it has gone out the door, I can't quickly check dimensions. I'm almost sure that the dimensions were very similar to what you have mentioned ? These struts were supplied by the customer and what I can tell you is that he bought them from a well known diy chain (B and Q)

I'm sure that for a pack of 4, he said he paid £7.99 and that included postage! Even if you were to buy them and they were no good you've not spent a fortune.

Just had a quick google https://www.diy.com/departments/dihl...3535612_BQ.prd