The biggest problem with Sichuan peppercorns outside south-western China is freshness. They quickly lose potency. I have surprised a number of European and North American visitors by serving them mala dishes using fresher peppercorns.
Even avowed Sichuan foodlovers have been astonished at the difference. They realise they've never really eaten them at their best.
Only buy in small quantities from a vendor with a high turnover. If they have been heat-treated, then game over - they are already dead.
As to ground Sichuan pepper, it isn't used that much, but when it is, it is ground 'to order'. That is, the home cook only grinds what they are going to use in the dish they are currently making. I've never seen anyone making a batch and storing it for later use.
Commercially ground peppercorns are worthless. Avoid.
