As a prior service Marine who is going to a new MOS school in the Army, when or how I will receive my uniforms?

So I was in your shoes a long time ago. Whoever the Supply Sgt is in the company or battalion (S-4) if you do not have a company supply sgt is responsible to issue you your initial set of uniforms. You cannot report to any schools without military gear they will drop you as soon as you check in. You should receive a packing list of everything that is needed for the school. Best bet is to contact your unit immediately to make sure your uniforms ect have been ordered in KYLOC.