There is this thing called as selling from your own inventory. Depending upon situation, it can be arranged, for a fee ofcourse.
And btw, the same applies to Pakistan as well. If India decides to ramp up its fifth gen with a 120 billion dollar infusion, what will Pakistan do? Rather what can Pakistan do?
Nothing.
So yes, India can indeed buy fighters like chocolates.
Who is going to sell you from their own inventory?
Is Russia going to sell u Su30 from its inventory while its production capacity has suffered due to war and what remains is being utilized/prioritized for its war effort?
Is France going to sell u Rafales from its own inventory while Russia has taken an increasingly aggressive posture and Trump is all about making NATO/Europe foot the bill and play a bigger role(in terms of money) rather than US?
Other countries that have bought the Rafale like Qatar…being rich…would they care to sell u from their inventory for money(which they have no shortage of btw)?
Are Greece or Indonesia or other Rafale operators(or who ordered ahead of India) going to prioritize India’s needs over their own defense needs? Look at the geopolitical situation facing Greece or Indonesia…no one is going to put u ahead of their own defense needs.
This isn’t a red light district in India…where u can have ur pick simply by throwing more money at it.
Same goes for increasing funding of ur own AMCA…pumping more money doesn’t mean you will have the product ready and in numbers.
If that was true China would have had J20 and J35 much sooner than they ended up having them. They provided all the necessary funding but developing indigenous capabilities like advanced metallurgy, material science(for radars, composites, radar absorbing materials/coatings, turbine blades, etc), advanced rocket motors for missiles, avionics, advanced understanding and modeling of aerodynamics, thermodynamics, etc.
…all of this takes decades of continued effort. It requires throwing money constantly and diligently for decades to educate ur population, conduct R&D at universities and by private companies(or even government owned research facilities), paying these scientists/engineers enough to prevent a brain drain…
…and then after lots of testing, trial and error…eventually there exists an industrial base that can churn out advanced defense equipment(or just advanced equipment in general).
U need to come out of this la la land that ur media feeds u about India is rich and because of it…all the other countries line up to please India and will do its bidding.