Dengeki Pikachu is easy to find, but expensive to get.
The easiest and fastest way to get it is from Amazon.com:
http://www.amazon.com/gp/bookseries/B00GDGDFI4/
The cheapest way to get it is from Amazon.co.jp:
http://www.amazon.co.jp/s/ref=nb_sb_noss/378-4476491-7001431?__mk_ja_JP=%E3%82%AB%E3%82%BF%E3%82%AB%E3%83%8A&url=search-alias%3Daps&field-keywords=%E3%83%9D%E3%82%B1%E3%83%83%E3%83%88%E3%83%A2%E3%83%B3%E3%82%B9%E3%82%BF%E3%83%BC%E3%83%BB%E9%9B%BB%E6%92%83%E3%83%94%E3%82%AB%E3%83%81%E3%83%A5%E3%82%A6
Some sellers on Amazon Japan offer international shipping, but it might be cheaper to use a deputy service since you'd get combined shipping then.
Here is a guide about ordering from Amazon Japan.
If you want to try using a deputy service you could try using
Yokatta or
Japonica Market. Those two are easy to use. If you can find another deputy service that has lower commission than Yokatta they will match and beat the other deputy service's fees (pro-tip: mention
FROM JAPAN's fees to Yokatta, don't use FROM JAPAN though, their service is quite bad as far as I have heard).
Also, be aware that the Japanese volumes contain
some censorship. Only the CoroCoro magazines The Electric Tale of Pikachu was first serialized in are completely uncensored.