There is a tendency among those critics who assign Justin's quotations to an uncanonical source to find that source in the so-called Gospel according to the Hebrews or some of its allied forms.

But a large majority of critics regard the Gospel according to the Hebrews as holding precisely this secondary relation to the canonical Matthew.
Justin's document can hardly have been the Gospel according to the Hebrews, at least alone, as that Gospel omitted the section Matt.
i.

18-ii.

23 [Endnote 103:1], which Justin certainly retained.

But it is within the bounds of possibility--it would be hazardous to say more--that he may have had another Gospel so modified and compiled as to meet all the conditions of the case.