Ah, sorry. Read too quickly. I would suggest looking at some of the large setting and adventure books by Frog God Games. I'm not familiar with Hackmaster, but if it is an OSR game, you could get the S&W version of the FGG material and it should be easy to convert on the fly.
They have adventures and settings for a variety of styles. There are over 120 adventures and setting running from short adventure modules and 600+ page books.
- Adventures and Tehuatl (Mayan/Amazon inspired theme)
- Adventures in the Borderland Provinces + The Borderland Provinces setting book (good for more sandboxy, bog-standard fantasy medieval fantasy game)
- Bards Gate (large city setting with some adventures, also a separate
- City of Brass (very large adventure and setting book that eventually take you to the City of Brass and its surrounds, you don't have to play it all the way through if you want to avoid higher levels (the revised S&W has rules up to level 20 and City of Brass eventually gets into the highest levels)
- Cyclopean Deeps. Set of two books, each hundreds of pages. Underdark style weirdness.
- Grand Duchy of Reme. A setting book. Has Rohan (from Lord of the Rings) vibes with some horsemen nomad clan elements
- Rappan Athuk. Megadungeon
- Razor Coast. Island hopping, pirate flavor. More early age of sail era fantasy
- Sea King's Malice. I don't own this one. I believe it is underwater based.
- Stoneheart Valley. Solid adventure path in a more contained area. Would be good to pair with Bard's Gate. More bog-standard fantasy.
- Tegel Manor. Remake of the classic 1977 Judges Guild haunted house and surrounding area. Can be run as a shorter campaign. I like it, but there were some issues with the maps.
- The Blight. Massive city state setting, higher level tech than typical fantasy. Grim dark: rotten, urban, degenerate city. Adventure path to uncover plots and threats from extraplanar incursions
- The Northlands Saga. Viking era inspired.
- Or you can just buy the Lost Lands setting book and a bunch of shorter adventures and piece together your own campaign from that.