IMG on a visa - really depends on what visa you are on. H1 is still quite possible. J1 is a tough deal. The reason being, many places that offer advanced fellowships(all are non ACGME accredited), the salary for the advanced fellow comes from doing screening colonoscopy usually half day every week. On a J1, one cant do independent screening colonoscopies whereas folks on H1 can do. For that reason, on J1, one is restricted to big name programs that have enough funds to sponsor the advanced endoscopy spot.
You may be able to get numbers as above by Shishi and probably do ERCP by end of three years if you get the numbers. It really depends on the institution that you train and volume. But 4th year advanced on J1 is extremely hard due to funding issue and your best bet is high level connections early on, in advanced field and doing some big panc/bili/bariatric projects