Where do I buy water purifier filters offline?

I want to replace my water purifier filters. Yeh water purifier waale sab loot ne ko baithe hai. An entire filter kit costs 1.3k online. I called and asked water purifier repair shops, none of them demand less than 3.5k. So I want to know if there is any place I can buy these filters offline, then I can ask them to only do the fitting part. I can buy online, but then it will arrive late, so I ask.