I'm located in central Louisiana (USA), and collected two specimens from UV light trap. My interested is small scarabs, so I barely know anything about Buprestids. I do not aware of any other ways to collect them.
I personally think Buprestis rufipes is one of the U.S.'s most beautiful beetles, and I'm a cerambycid/scarab guy!
I've only collected a few over the years, and all but three were collected on the trunks of old, dead beech trees. They are often perched high on the trunk (8-12' or more), and I've probably missed twice as many as I've caught due to that behavior. I took one as it flew about 6' off the ground, another in a fermenting bait trap, and one being carried by a Cerceris wasp.
The specimen taken by Cerceris was the first buprestid I ever collected - at the age of 14. That specimen is still a sentimental one for me! Cerceris has been studied extensively recently as a predator on Agrilus planipennis - emerald ash borer. Look for a population of these wasps in open, sandy soil - there are often dozens of burrows in close proximity to one another. One good place to look is baseball diamonds located near natural woods. The wasps like the outer edges of the infield. Simply stand in the area during the heat of the day and watch for wasps returning from foraging, carrying a beetle. Sweep the wasp out of the air, shake the net to get it to drop the beetle, and then release it - your beetle will be in the bottom of the net, paralyzed. In a single event of about 2 hours, I collected over 30 buprestids this way, including the Buprestis, as well as numerous Dicerca and Chrysobothris. I stumbled upon this method as a kid in 1974, but it's now being used to monitor for Agrilus by hand-collecting the Cerceris and "stealing" their prey.
I've seen a number of them in Lindgren funnel traps over the years as well...
When you say 'small scarabs' - which group are you referring to? While I'm primarily a 'bycid guy, I collect Nearctic Scarabaeoidea as well and have an interest in Melolonthinae, especially Phyllophaga, Serica and the like, as well as the Aphodiinae. I'd be interested in learning about your interests...
I do not collect beetles, as a matter of fact, I dislike them immensely. They get into my light traps and tear up my moths. However, I have friends and associates who suffer from Coleopterism. As a result, I retain most of the larger beetles, especially Scarabs, Long Horns and really large ugly beetles for my friends and associates. (Have you ever noticed the first three letters in associates. It explains a lot!)
As for Buprestid, I manage to collect several every season in my bait traps and then only in the Slotted Pan Type. I also managed to find them on the ground. I assume the fall out of trees as I have had several hit the ground in front of me will walking along woodland trails.
Several years ago I collected one in a Pheromone Trap for Sessidae moths.
The only time I ever found them in any numbers was at the lights of a gas station along I-40 in western North Carolina in the early 1980's. There were lots of insect in general, including moths. I have a friend who is a Coleopterist and is the beneficiary of most of the Coleoptera I find/collect. I have given him the vast majority of the beetles.
An area where I have found Buprestid beetles recently and in some numbers was in southern Indiana in Harrison County.
Supposedly they are not common anywhere. There is also one of those large reddish brown beetles with huge Mandibles and another destroyer of moths in my light traps.
I have collected two specimens of B. rufipes here in Ohio, both from beating. One was taken from a large beech and the other was found on my beating sheet after thrashing various hardwoods including oak and hickory. It was stuck up in one of the pockets in the corner of my sheet. Beautiful beetle for sure.