Quite common during the Gettysburg campaign for the Federals, since their supply bases were being shifted as they maneuvered to catch Lee. However, their problem was temporary, lasting at most a few weeks. In the meantime, the Confederates were "requisitioning" large quantities of shoes from Northern towns, and they also obtained a large supply from dead Federal soldiers after the first day's battle.
Some sources (dates are all 1863):
(Charles Mattocks, 17th Maine) June 30, we are suffering for shoes in the regiment. Some men are actually barefoot. A supply has been expected for the past week.
(Jamie McNeil, 40th New York, letter) July 30, there are some in my regiment with no decent clothes to wear, many with no shoes.
(Lt. Col. Sherwin, 22nd Massachusetts) Our baggage is 20 miles in the rear. Yesterday a third of the men have no shoes, and feet very sore besides. Today, July 10, we are supplying them.
(Col. Oliver Edwards, 37th Massachusetts, post-war report) The march was very severe and many of my men on the route from Fredericksburg had marched their shoes off their feet.
(28th Pennsylvania, History of Pennsylvania Volunteers) July 11, many of the men were barefooted and suffered considerably during this march of more than 75 miles. On July 18, near Sandy Hook, the regiment was provided with shoes and clothing.
(Quartermaster Dennis Tuttle, 20th Indiana, Westminster, Maryland) July 5, went out yesterday morning for forage and shoes.
(139th Pennsylvania, Pennsylvania at Gettysburg) After men of Co. I's shoes had worn out, they tied up their feet in cloth to protect them from the hot sand and tramped cheerfully on.
(154th New York, Newspaper Clippings, NY Military Museum) July 9, the men drew clothing, of which they stood in much need, especially of shoes and stockings.
(O. W. Norton, 83rd Pennsylvania, Army Letters) July 21, thousands of men were barefoot, officers, too.
(Lt. Oscar Ladley, 75th Ohio) July 9, the men are nearly all barefoot.