Frist off... what are your stats? height, weight, body fat, program, how many cals youre getting in now?
And to answer your question, alot of people have this problem, and one way of getting in extra calories is liquid calories. Grow! is great, as is Metabolic Drive, but I'd suggest Grow! since its got carbs and you're bulking.
The cheaper way out is milk.
Also, calorie dense foods, nuts, pb, oils.