It's even worse than trying to find the acid content of a particular maltster's acid malt. It's not even consistent from batch to batch from the same maltster. It may not even be consistent within a batch, given the way it is made. Bestmalz specifies a "wort pH" range of 3.5 to 4.5. By wort pH, I assume they mean Di pH (i.e. pH in distilled/deionized water). That's a pretty wide range. Unless there's a desire/need for Reinheitsgebot compliance, I personally think acid malt is an odd way to go about acidification, because of the lack of precision.
The good news here is that with 88% lactic acid, you should be able to get a more consistent mash pH than you were able to get with the acid malt. I'd recommend assuming you had been getting about 2.5% acid by weight (a nice middle-ish value to minimize the potential error), and go from there.