[glend (Glen)]

This question also puzzles me as finding a guide star is often a frustrating process for me with a dedicated and adjustable guidescope. True the size and f ratio of the guidescope is a limiting factor and the larger aperture of the imaging scope gives greater reach but your always limited to the FOV. Additionally, in light polluted skies, guide stars can be harder to find. My solution that I built into my 10" imaging newt , was to get the Skywatcher guidescope mount which gives good x and y axis control to independently source a guide star. The guidescope mount provides a very large area to find a suitable star. Unfortunately the penalty for that wide field adjustment is weight, the guidescope mount adds about a kilo to the overall weight on the mount/scope. Once you add a larger aperture guidescope the weight goes up again. I use a ZWO 60mm guidescope, which is lightweight and can mount directly on the guidescope mount. As my 10" scope is light the additional weight is not a significant factor and actually assists balance by where I located it. I believe this is a good solution for light newts but would be not so good where your approaching the imaging capacity limit of your mount.
It is also easily moved to other scopes regardless of configuration as long as the weight can be tolerated.