Hi diamondshopper,
Nice to live close to the border and have the ability to get products without paying large international shipping fees. 
It is difficult to find specific foam blocks like that. More people use the 31 ILD for transition layers, I suspect. Offhand I know that some, like Luma Sleep, uses Qualux layers, not sure if its the 2.8lb 41ILD Qualux. Qualux is a “family” of polyfoam made by Carpenter with high resiliency characteristics (low hysteresis or energy loss) and can range from 1.5 lbs to over 3 lbs. Qualux Ultra is an actual HR polyfoam with similarities to latex in terms of performance. Do you know if you are looking for Ultra or regular Qualux? As far as the Lux-HQ Foam product from FBM you mention they list it as 2.8 density at 50 ILD (@ 25% compression) see the product Physical Datasheet here.
I would be a little cautious about Foam by mail (FBM), as many people on this forum have commented about in the past, probably some level of risk not “exact product” you are looking for. Most comments were about the US branch of FBM but I would read through this thread and this thread, and some of the associated links and place a phone call to ensure accuracy.
If you have any other questions, please let us know.
Phoenix