You can make some!
What you'll need:
1. Insulation board from home depot or menards
2. Aquarium-safe silicone
3. Dry-lok paint
4. Quik-crete cement color
5. Torch or heat gun
What to do!
1.Cut out foam to look like steps, adhere together with silicone, let dry for 1 day.
2.Carefully torch edges to smooth it out make it look more natural
3.Mix the color of choice of quick-crete, mix with dry lok.
4.Paint! Use multiple layers, let each layer dry for 1 day before adding another
*be sure to paint all sides, as the dry-lok acts as a sealant.*
5. Once you're happy with how it looks, TAKE YOUR BETTA OUT OF THE TANK, and make him situated with a temporary tank that he'll use for a few weeks.
6. After emptying the desired tank, silicone the bottom and side of stairs that you'll be adhering to the tank.
*be sure to get the edges or bacteria can build up behind it*
7. Once let sit for 2 days before adding water
8. Fill tank, do frequent water changes to be sure pH doesn't get out of hand. Once levels are safe, add your fish:)
OR, if you don't want that much trouble, get some smooth aquarium safe rocks, and make stairs out of those using the silicone. :)