This is only a solution or more likely a workaround for those their achievement is bugged or the tracker isn't working (credits to Powerpyx)
1- Play in Offline mode Reroll a new Adventure mode in Yaesha, making sure that The Red Throne is your starting location.
2- Go straight ahead into the building and open the gates to talk to the Queen. Make sure you don’t get her angry. Be kind and reverent.
3- As you go through the areas you visit, follow the main quest marker until you can fight against the Corruptor/Many Faces.
4- Warp back to the Red Throne world Stone and enter the Queen’s Room. Kneel when given the option to receive the Seal of the Empress Ring
5- Now make your way back to the World Stone, but enter the room on the right. In here, position yourself in front of the slate of stone where you can see the icon of the Queen on the floor and equip the ring.
6- Drop down to find Ford’s Scattergun.
7- Go back to Ward 13 and reroll to obtain the same starting area as in Step 1.
Repeat Step 5-7 five more times.
With a bit of luck you’ll unlock 15 guns achievement after collecting Ford’s Scattergun +5. As for 30 Guns achievement, go back to Ward 13, buy as many guns as you can at Brabus’. With a bit of luck, you’ll also unlock the achievement for owning 30 guns.
IMPORTANT: There may be a chance that the tracker doesn't track handguns (which did happened to me) I found a solution for this, it takes time but it unlocked the 30 Guns achievement in the end.
1-Play in offline mode and reroll a new Adventure mode in Losomn, making sure that The Morrow Parish is your starting location.
2- Go through the till you reach the Clock tower area, the asylum is near, go till you reach the asylum.
3- Go inside the asylum and go till you reach the ground floor, there is an office with a safe inside, enter the combination : 2971
4- Collect the Double barrel handgun.
5- Return to Ward 13.
Repeat steps 1-5 five more times.
Hope this helps and if anyone knows a handgun faster to obtain, please let us know