Hi Morgan - it may be that you are trying to blend to the surface isocurves - these indeed do not exist, as curves in the file, they are only properties of the surface and displayed on screen to help visualize the surfaces. The successful blends in your file have come off of the radial edge curves - these are also part of the surface but are generally accessible to commands that require curves.
To get what I think you want, you can use ExtractIsocurve using the ‘Quad’ odnap to extract radial direction isocurves that will respond to BlendCrv, or use the Edges option in BlendCrv to force the blend to come off the surface edges at 90 degrees.(Quad osnap as well). I’ll see if I can make you an example.
@Morgan_Ruben - see if the attached is what you are after - red = ExtractIsocurve, blue = BlendCrv, Green = BelndCrv with Edges option.
tryout7_3dtextures_PG.3dm (97.9 KB)
-Pascal