You say:
According to the Exodus 35:23 (New American Standard Bible)
” Every man, who had in his possession blue and purple and scarlet material and fine linen and goats’ hair and rams’ skins dyed red and porpoise skins, brought them.”
And according to my NIV bible for the same verse, it says,
“Everyone who had blue, purple or scarlet yarn or fine linen, or goat hair, ram skins dyed red or hides of sea cows brought them.”
My question is: Weren’t the Israelites stuck in the middle of the desert when they built the Tabernacle? Where on earth did they get porpoise or sea cow skins?
The Israelites would have carried a lot of the materials for the Tabernacle out with them from Egypt. We know that Moses had asked the people of Israel to ask the Egyptians for silver and gold jewellery and for clothing. These were given to the Israelites in large enough quantities for the Exodus record to state that they plundered the Egyptians. See Exodus 12:35-36.
The people of Israel had also done as Moses told them, for they had asked the Egyptians for silver and gold jewelry and for clothing. (36) And the LORD had given the people favor in the sight of the Egyptians, so that they let them have what they asked. Thus they plundered the Egyptians.
Also, even though the people of Israel were in the wilderness, if you check the map of possible routes, they were often not far away from the Red Sea, especially if Mt Sinai/Horeb was east of the gulf of Aquaba. We read an interesting comment in Easton’s Bible Dictionary
The dugong, very plentiful in the shallow waters on the shores of the Red Sea, is a marine animal from 12 to 30 feet long, something between a whale and a seal, never leaving the water, but very easily caught.
The Israelites could conceivably have sent hunting parties out to get the porpoise/dugong/sea cow skins, although nothing is mentioned about it. Exodus 35:21:23, tell us that these items for the tabernacle were donated by those with a willing heart.
And they came, everyone whose heart stirred him, and everyone whose spirit moved him, and brought the LORD’s contribution to be used for the tent of meeting, and for all its service, and for the holy garments. (22) So they came, both men and women. All who were of a willing heart brought brooches and earrings and signet rings and armlets, all sorts of gold objects, every man dedicating an offering of gold to the LORD. (23) And every one who possessed blue or purple or scarlet yarns or fine linen or goats’ hair or tanned rams’ skins or goatskins brought them.
So whether all these goods were brought from Egypt or whether some things were gathered along the way, we cannot really tell.