There is no tool to create an equidistant spline entity.
You can produce a similar effect by converting the spline into a polyline and using the polyline equidistant tool:
Copy the original spline entity for future reference as it will be destroyed in the process.
Explode the spline:
Select the splineConvert the loose segments into a polyline:
Choose "Modify - Explode"
The spline has been exploded into small line segments
Choose "Draw - Polyline - Create from Segments"Use the equidistant polyline tool to create an equidistant polyline
Click one of the exploded spline segments
The spline is now represented as a polyline
Note that this is not an exact equivalent of an equidistant spline, but it might suffice for some purposes.