Good question. As far as I am aware you can obtain a share cert for any company listed on the London Stock Exchange (LSE). Your broker may charge you an additional fee and you can check beforehand. Investment trusts are companies so no different than any other company in that regard. You should call the client services department of the stock broking company you have your account with. If they are unsure, ask them to find out definitively.
Hope that helps
Rory Gillen