Backend: add explicit URN handling to resolve CivitAI model/version into a direct download source; normalize and accept a `sources` parameter (local, huggingface, civitai, all) and drive per-source searching. Reorder and tighten search logic (local/popular, model-list, HuggingFace, CivitAI) and include `searched_sources` in results and improved logging. Frontend: add per-missing-item search result cache and state, UI buttons to pick search sources, merge incremental results instead of overwriting, show selected-source helper text, pass selected source to the server, clear cache on refresh, and improve search status messages and UX. Overall: enables targeted online searches, preserves previous results, and surfaces direct CivitAI downloads for URNs.