About 360 domestic companies have been awarded work valued at about £157 million out of a total of £393m handed out so far, the Scottish Government revealed.
Scottish businesses won £72m of the £104m total for supply orders and £85m out of the £289m value of subcontracts, with about 80% of all procurement now complete.
Transport Minister Keith Brown said the overall project was having a positive impact on businesses. About 92% of the supply orders went to Scottish companies, he said.
But Labour infrastructure spokesman James Kelly said: "The reality is that not enough of the total contracts let have gone to Scottish firms.
"The rest have gone overseas, which is a massive blow for our home-grown businesses."