Most wallets, as far as I know, have an option to rebroadcast a transaction. Some of them do it automatically, while others require you to do it manually.
Plus, you can use some of the public services, like https://live.blockcypher.com/btc/pushtx/ or https://blockchair.com/broadcast, or the so-called "free transaction accelerators" that will do it for you.


I dont know of any. Due to the decentralized nature of the blockchain (each node maintains its own mempool), Im unsure if such data can even be collected reliably.