Paul McCartney’s post Beatles exhibit at the Rock & Roll Hall of Fame has hit a road block. The museum’s upcoming exhibit “Paul McCartney and Wings” is opening on May 15 , but we hear some of its artifacts are having issues getting to Cleveland. Seven of McCartney’s guitars have been stuck in customs in London due to the Convention on International Trade in Endangered Species (CITES). The famed string instruments are made out of Brazilian rosewood, which is one of the most rare and endangered trees on the planet. “They’ve been stuck in London customs for a month,” an insider told Page Six. Paul McCartney’s prized guitars have been stuck in customs in London for over a month. WireImage Seven of McCartney’s guitars have been stuck in customs due to CITES. Getty Images “The tree is endangered so you can no longer use it, but it’s the best wood you can use for sound and acoustics,” they added. The guitars are a part of McCartney’s personal archive.…