Yes, you need a separate visa, either H1 or O1. H1 is difficult due to the quota, O1 is difficult because it requires fairly outstanding qualifications (distinguished fashion model in the industry, including titles in widely-regarded contests of first rank, magazine photos etc). For H1 you need a waiver for any HRR that might be attached to your J1 visa. For O1 its not necessary. To participate in "cultural events" there is a special visa category (P-3), but that probably doesn't apply to you since you seem to be looking for fashion work and not dance/art performances, if I understood you correctly.