Some things to look into:
For drawing any number of equally-spaced interval objects between single Lines or single-line-segment Polylines, you can use SplitBetween.lsp with its SLB command, available here.
For longer/convoluted paths like your contours, to draw one "average" path between two of them, you can use PathAverage.lsp with its PAv command, available at this post. That might be amendable to do multiple paths in between.
Read the other posts on those threads to understand what some of the [significant!] difficulties and complications are. [There's also SplineAverage, but that requires Spline objects, and with the same number of Fit Points.]
BUT I can't help but wonder.... Many of the yellow intermediate contours that are already in your drawings are not anything like equally distributed between the red ones. There are a few clustered closer together toward one red contour, with a wider spacing or two in the middle, and a narrower one again closer to the next red one, etc., and twists and turns much odder than simply unevenly-distributed spacings. This variability in contour is certainly characteristic of real-world situations. So filling in equally-spaced "contours" between others can't possibly be a genuine representation of the actual "lay of the land." If the red ones are "known" but nothing is known specifically between them, what is the purpose of faking something? Couldn't it lead someone astray, if they're [for example] basing calculations about things like cut and fill on a presumed regularity of slope between known contours that has no basis in reality?
Kent Cooper, AIA