The answer to your challenge is in many of these threads.
Italy abandons africa and uses tank/mech pairs and its air to kill blockers and ensure the Russians cant stand behind the front lines with a counterattack force (the can opener)
Germany relentlessly stratbombs the russian factories (Italy and Japan can easily join in, bombing “around the clock” before and after the russians turn)
Japan takes all the russian money it can starting turn 1 and just needs to make sure their capital doesnt get taken–low risk no odds battles are required to pull this off.
These, plus a G1 done correctly (no UK navy wipeout) can mean that you are ready to defeat Moscow on G5
Eventually the Italians and Japanese can start landing large defensive and offensive air forces into German territories so the counterattack possibility is further weakened
All 3 axis “hail mary” and make relentless attacks against the TUV trade with the goal of defeating moscow which is typically not something the Allies can counter until turn 7-8 no matter what they do or buy (dave will often sacrifice over 100+ IPC worth of japanese planes just to kill 6-8 russian defenders because then Germany finishes them off)
Weaker Allied players will continue to nibble at the edges rather than throwing everything they can into the defense of moscow
And finally, with a bid under 20-30, even if Moscow can itself be preserved by extraordinary means (UK all in via persia, USA all in via bomber streams), Russian income is gobbled and once it falls below 15+ IPCs it cannot make counterattacks or fight a war of attrition.
While I’ve focused on KJF in the last year, KGF is the only way to delay germany’s direct assault–you may be able to get germany to spend after G4 in pure defense, but either way–the units needed to take moscow are all built before G4 and later turns can all be used in defense or just to buy Stratbombers and seal the deal. If moscow isn’t defeated by the Germans, the Japanese take its money and destroy it from behind.