Very little information to go on, I think you might want to describe your stairs in more detail if you want replies...

Did you try one of the external models on the Support: 3D Models page?

OR create a structure with boxes (and possibly sloping walls on the sides)?

OR have a go at designing one for yourself with SH3D (draw walls similar to the stairs lying on its side, set wall height = stairs width etc., export to .obj, then import and flip). See recent post - 3 ways to create a simple stair for different methods with step by step explanation.

ok