3000 series were out of stock because they were extremely cheap. Now that most ppl bought those things, the market is already filled with 3000 series cards and ppl don't upgrade each gen. So it is quite possible to get one.
Rtx 40 series is just overkill. I run RTX 3060ti but for 3070ti is future proof for the next 3 years so get that instead of spending astronomical amounts on a 40 card
im pretty sure the price gap between the two is like 2k, and you WILL be bottlenecking your CPU with a 40 card guaranteed, so would also need a new CPU, and even then I think the best CPU's on market still bottleneck the 40 cards