Where to find LP clamps?

A good-quality, inexpensive clamp which can be used with just about any standard, non-threaded spindle is made by England's J.A. Michell. The black-colored version is a lightweight design made of non-resonant Delrin with a knurled-aluminum-knobbed collet mechanism for secure fit, and you should be able to get it from Michell dealers for around $45-$50. It made a definite sonic improvement on my 'table, most notably in image focus and transient articulation, and of course they help with less-than-perfectly-flat records. However, before clamping your records, make sure you're using a mostly flat-surfaced mat which effectively damps the platter and doesn't reflect energy back to the stylus/groove interface.

Marakanetz, I have to take exception IMO to your description of firm clamping as causing a 'vast sacrifice of details'. The HF attenuation you hear is the reduction of spurious resonances in the record itself, which although sometimes regarded as adding pleasant (if inaccurate) 'air' to the presentation, are not increasing transparency to recorded detail - on the contrary, they're reducing it.

M., you are correct in pointing out (as I also referred to in my first post) that the platter/mat situation makes a difference in these regards. In addition, I do think it is possible in some instances, with a soft mat and a thin-vinyl pressing, to 'over-clamp', deforming the record and placing it under stress. Although I doubt that the light weight of the Michell clamp by itself, untightened and acting merely with gravity, could have much of a positive effect (in fact, it could have a deleterious effect if allowed to vibrate), at least we agree that it is a good clamp at a low price.