I was getting 140Mhz out of 8ns PC-100 with just aluminum plate spreaders on back in the day. That was before they were cherrypicking and rebinning for 7.5ns "barely" PC-133 though and PC-133 had 7ns. (i.e. the pool of 8ns parts had parts that might otherwise have been binned 7.5ns.) But yeah, depended a lot on airflow in your case, particularly bad if you had a PIII or tually overhanging the RAM off a slotket and the spreaders might have been collecting heat rather than getting rid of it.
Source of generic, module sized (as opposed to high rise with frills and flounces... oh, ineffective notchy fins) spreaders might be ECC server RAM, which goes by the bucket load for cheap.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.