I buy Singapore here:
https://www.singaporemath.com/They've also got forums and a list of errata.
In addition to the text/wb, we use IP and CWP.
We'll be switching away after finishing 5B (Standards edition). I'll still go through IP and CWP for 6, but we won't use the text/wb for them.
We'll either move to AoPS (Art of Problem Solving) or do more with Elements of Mathematics
http://www.elementsofmathematics.com/I used these textbooks when I was in middle school and they're excellent. It's definitely not traditional math but it is very much real math.
