I have looked on FindMyPast and the IGI and the information seems patchy. You may never get exact information because it would depend on whether the parents had their offspring baptised shortly after they arrived, or in a few job lots.
FMP - 1751 - 1765 - there was a couple, Samuel & Rebecca, who had a huge family in Dursley, no Thomas. 1789 - 1797 a John & Mary were producing in Dursley, again no Thomas. So if anything, these weren't the ones you want. Odd baptisms in Coaley and Stinchcombe, no Thomas.
IGI - a Thomas & Mary [Essex] in Avening (near Tetbury). They married on 4 Feb 1778 and produced offspring Ann bp 20 Sep 1778, Dinah 15 Oct 1780, Thomas 6 Oct 1782, Samuel 5 Mar 1786.
John Sansome & Mary Millwaters had a huge family in Horsley, Nailsworth, 1759 - 1777ish, including a Thomas bp 1765 [Batch P018101], but they seemed to have had their children baptised at regular intervals, so perhaps 1765 would be too late for yours.
There seems to have been a substantial presence in the Stroud district, but I can't spot your Thomas.