Peco's 9 inch radius settrack turnout is still available. A turnout's number is based on the number of "units" of straight track in relation to curve track starting at the "frog" of the turnout.
The frog is the part where the two inner rails join together.
For example: If a turnout extends 4 units of straight length on the inside rail from the frog and, at that point, the diverging inside rail is 1 identical unit of length from the straight rail, you have a #4 turnout.
The Atlas #4 turnout has a 19" radius curve and I am not sure what radius of curve is on the #6 turnout.
Atlas, Micro Engineering and Shinohara list their turnouts by number, while Peco lists them as Small, Medium and Large while their actual radius is listed in their cataloge.
Peco's Setrack Turnout (Small) is 9 inch radius, while their streamline Turnouts are as follows:
Medium: 18 inch
Large: 36 inch
Medium Radius "Y": 30 inch
Curved Double Turnout: (Inside) 18 inch, (Outside) 36 inch.
For their Code 55:
Small: 12 inch
Medium: 24 inch
Large: 36 inch
Medium Radius "Y": 24 inch
Curved Double Turnout: (inside) 18 inch, (Outside) 36 inch.
BTW, All these measurements are in N Scale
Hope this helps and have a great day

.
Cheers.
Terry