Hmmm....starting to get something. Look at this quote from Urith: a tale of Dartmoor, by Sabine Baring-Gould, 1890 (page 40):

Come my lads let us be jolly
Drive away dull melancholy
For to grieve it is a folly
When we're met together

So my friends let us agree
Always keep good company
Why should we not merry merry be
When we're met together

---

And another book by Sabine Baring Gould (1891), In the roar of the sea, page 369:

Water drinkers are dull asses
When they're met together
Milk is meat for infancy
Ladies like to sip Bohea
Not such stuff for you and me
When we're met together

---

Oh, and yet another book by Sabine Baring Gould (1898), An old English home and its dependencies, page 331:

Here's the bottle as it passes
Do not fail to fill your glasses
Water drinkers are dull asses
When they're met together

Milk is meet for infancy
Ladies like to sip Bohea
Not such stuff for you and me
When we're met together

---

The song is also mentioned on page 338 of The Singing Game by Iona and Peter Opie, who speculate that "Come My Lads" may be an ancestor of the children's song, "Mrs. Macaroni:

Here comes Mrs. Macaroni
Riding on a big fat pony
Looking for a house of glory
This is Sarah's wedding
Om pom Susianna,
Om pom Susianna,
Om pom Susianna,
Mrs. Macaroni

---

Oh, look - Roud does has the song, listed as Come My Lads. I think that proves it may not be an American Grange song.....
The most promising citations from Roud are these:

• Hitchcock, Folk Songs of the West Country (1974) pp.28-29
• Williams, Folk Songs of the Upper Thames (1923) pp.54-55
• Graebe, Come and I Will Sing You (2010) p.7

It's also in the Sabine Baring-Gould manuscript collection at Take Six, which is the best source of all.