Hey TriStar500. I read some Japanese, so I've gone through their website, and the JAS website.
From what I could gather:
They don't mention anything about the two aircrafts you asked. I believe their planes are all ex-JAS. It might be a few years before any of the "rainbow sevens" (JAS 777s) are handed down.
Harlequin Air was established in January 1997. They operate international charter flights out of "local" airports . In other words, airport other than Haneda, Narita or Kansai. JAS "wet-leases" Harlequin MD81s (total 4) on some domestic routes, operating in and out of Fukuoka.
Harlequin used to have a DC-10 (delivered to JAS in 1990 I think), which retired last year. The only A300-600R is wet-leased to JAS for Japan-China routes, and also operates the charter flights.
In case the term's not widely used: "wet lease" here means Harlequin's crew and planes operating JAS services. "dry lease" would be just the plane.
Some of the charter destinations: Brisbane, Sydney, Christchurch, Vancouver, Calgary, Paris, Kathmandu. Harlequin hires a lot of ex-nurses/babysitters as FAs.