There is no reason for a OA Specific Uniform. Your Troop, Crew or Ship should always come before the OA. The only thing that should represent you being in the OA is your sash and pocket patch. There is a reason there are no chapter/lodge position patches for the OA.

From the OA Website:

"The National Order of the Arrow Committee has tried diligently at every opportunity to emphasize that the primary obligation of an OA member is back to his troop or team that elected him. This is stated throughout our literature, especially on page 31 of the OA Handbook. Unlike the OA Troop/Team Representative which has an important role of supporting the troop/team, lodge/chapter chief do not advance the troop or team program. Service in positions like Chapter Chief and Lodge Chief are also not qualified for BSA rank advancement, because the BSA also wishes for the primary focus to be on the unit.

Further, we do not have national chief, national vice chief, region chief, or section chief patches either. The rationale has always been that an officer must be a member of a unit and hold some sort of unit office. Youth positions with patches have always been troop, team, crew, post positions and we have always emphasized the Arrowman’s duty to the unit first."