Regarding "collar tabs" do you mean officer related, officer of the 148th Infantry Regiment, or anything related to the Regiment? All of the metal insignia, (rank, U.S., branch devices) were distinctly different for enlisted and officer. The most difficult item to obtain would be officer infantry branch insignia with numerals "148" assembled. In regards to the officer collar insignia it would be far easier, and less expensive, to obtain plain (without the numerals) infantry collar insignia. The shoulder sleeve insignia, which was not generally worn until after the Armistice, should be for the 37th (Infantry) Division. No doubt sometime before he was discharged your man probably worn that SSI, or if transferred to a higher headquarters, the SSI representing whatever command he was assigned to. It is possible he may have changed branches, but if you intend to stay with insignia related to the 148th Infantry Regiment, whether he changed assignments would be irrelevant.

If you don't have any documents on your subject you should try to get what is available of his service records from the National Archives to get a better idea of his assignments, and etc.

There are a few sites that provide replica material for reenactors, that may be a source for displayable items, that could be obtained at a reasonable cost.