Metford drops in infinity missions only, as you've figured out.
The drop locations for this item are as follows:
1-99 Parum 1 creatures (Badira, Go Badira, Jaggo, Polty, Stingee) in the VR Wilds map at a rate of 1/374, affected by drop rate modifiers.
100-250 Bysha Type-Koh21s, any map, at a rate of 1/200, this is not affected by any drop rate modifiers.
When it comes to the Infinity Discord, it did require you to accept the rules, and then wait 10 minutes before you were able to post, although I've removed the 10 minute cooldown as I don't think it deters bad actors or bots anyway, so this isn't an issue anymore if you wish to rejoin. The link, along with other useful info, can be found on the PSP2i Wiki homepage at the (incomplete) PSP2i Wiki.
Furthermore, drop information can also be found on the very useful datamined drop spreadsheet, compiled by Mewn and Agrajag of PSUMods. You will need to make a copy of your own to be able to filter it. For information about how drops work, please refer to Mewn's write-up here.