--snip--
Never checked, but don't some of the block explorers have API calls for this?
Some block explorer definitely offer such API, but obviously you need to trust them and it's possible they have certain limit (e.g. maximum call per minute).
The issue is going to be with the mempool being well over 900MB that a lot of places / nodes are going to be dropping different transactions depending on their settings. I they have the default 300MB you may get a different answer then if they have it set to 512MB and that may be different then 1024MB.
So unless you know what they are doing querying one will only get what they have in theirs.
-Dave
There's also problem with whether they store transaction which was replaced through full RBF and transaction broadcasted more than 2 weeks ago.