Hey there. Congratulations on the K-01!
The problem is that Pentax right now isn't making any primes in the range between the 21mm and 35mm. And the Pentax 14mm, 15mm, and 21mm are all relatively expensive. (as are the 10-17mm and 12-24mm) Although, a lot of members love the 21mm on their K-01. You can try to find an older FA 20mm.
With Pentax, you can get ancient manual lenses between 24mm and 300mm pretty easily, and they are often relatively cheap. But wider than 24mm becomes problematic because some decades ago, ultra wide angle lenses were very hard to design and often not of great quality. And 24mm on APS-C is not all that wide, even though it is still significantly wider than 35mm. There are plenty of old 24mm and 28mm lenses out there, Pentax and other brands. Feel free to
search the lens review database.
Sigma makes quite a few wide angle zooms that are decent quality, like the 8-16mm and 10-20mm (two versions, check
here for details). Tamron has a 1
0-24mm lens.
You might also be interested in replacing your 18-55mm with the Pentax 16-45mm lens (overall better quality, wider angle).
Another option are the Samyang lenses. They are fully manual and might not be very easy to focus on the K-01 at first, but you get the hang of it eventually.
Samyang right now has the 14mm f2.8 lens, the 16mm f2.0 lens (just been released), 8mm fisheye, and I think they will soon release the 10mm prime. These are usually very good optically and have a sturdy construction. But uncalibrated focus rings are common, and they have no automation, except auto-aperture. I have the 14mm, but its kind of hard to focus the K-01, so I prefer to use it on my K-r (its hard to focus because on the LCD screen "everything" looks in-focus, even though it isnt really)