In my Realms campaigns, there has always been at least one encounter that included another party of NPC adventurers.
I prefer to start in Cormyr, so adventurers aren't hard to find.
All of the above, including the Society of Stalwart Adventurers in Suzail, laws requiring weapons to be secured by peace strings and the purchase of a charter from the Crown by an adventuring party.
Additionally, one can find bards, factors representing nobles and merchants, spies from other lands, agents for various non-human power groups (illithids under Arabel, the Xraun beholder hive encircling Cormyr, etc.) and representatives of cabals all hiring adventurers openly and in secret (through intermediaries).
Lots going on.
I prefer it when the characters encounter dead adventurers. It's a great way to warn the PCs that somebody else tried and failed, to hook the PCs on the potential to recover adventuring gear, and provide clues and opportunities for detective work by the PCs when they search the dead adventurers and listen to my descriptions of what their characters see.
