Police found two sub-machine guns and ammunition after carrying out raids across the region to tackle on ongoing feud between travelling communities, which saw two teenagers' skulls being stolen from a grave.
Up to 150 officers from five forces across Northern England were involved in the raids at travellers' sites.
Durham Police, who led the investigation, said two sub-machine guns and ammunition were recovered in South Yorkshire. A small handgun was also found at a site.
The macabre act at Metal Bridge Cemetery, County Durham, was the latest in a series of shocking incidents involving two factions of the travelling community, police said.
The swoops on travellers' sites and homes in Doncaster, York, Middlesbrough, West Rainton near Durham, and Gateshead were aimed at getting more information about the feud.
Dogs trained to find dead bodies were used to try to locate the stolen skulls, which belonged to brothers Levi George Price and Gareth Price, who both died aged 16, in 2001 and 2005 respectively.
The theft was carried out to antagonise arival faction, police believe, and has sickened the majority of travellers.
In total seven have so far been arrested for conspiracy to commit GBH.
Detective Superintendent Adrian Green, leading the inquiry, urged whoever has the skulls to give themselves up.
"Your community is appalled at what you have done," he said.
He thanked travellers for coming forward with information since Monday, when news of the graveyard attack broke.
Chief Inspector Caroline Dawson works in Darlington where in recent weeks a home has been petrol-bombed and two others badly damaged after being rammed by lorries.
She said the majority "want to live a peaceful life".