With some advice from offgrid I’m looking for a 40MOA base for my Bergara bolt action in .22LR. I’ll be shooting out to 400yrds and the scope has 25mil elevation available.

As RichardC states above, EGW has the bases for about $70. Nightforce's version runs about $120.

Your scope has 25 mils of elevation, which is about 84 MOA. Depending on your ammo, MV, and DA -- your elevation requirements for subsonic at target distances, with a zero of 50 yards might be about:
70-74 MOA for 400 yards
56-60 MOA for 350 yards
44-47 MOA for 300 yards
33-35 MOA for 250 yards
23-25 MOA for 200 yards
14-15 MOA for 150 yards

Which means with a 40 MOA base and a zero at 50 yards, you can dial all the way out to 400 yards without using hold overs/unders. However, your zero will be quite close to the limits of the scope's elevation, which means your optical quality won't be as good as it is near the center of vertical adjustment.

Consider the distances at which you normal shoot. If the majority of your targets are in the 50-250 yard ballpark, then you might consider optimizing results for those targets -- which means a base of 20-30 MOA. And if your scope has a good reticle for holdovers, you might consider holding over for targets of 350-400 yards.