I have come from England, where avocados are available all year long, to Israel, where it is primarily a winter-spring fruit. Do I recite Shehecheyanu upon eating it in Israel? Answer:
Let us start with some background. The beracha of Shehecheyanu is a proper response to the happiness of something enjoyable returning to our lives. Regarding produce, Shehecheyanu applies only when there are distinctive seasons during the course of the year (Shulchan Aruch and Rama, Orach Chayim 225:6). The Rama continues that for this reason we do not make Shehecheyanu on a vegetable, "for it stands in the ground all year." He expounds elsewhere (Darchei Moshe, OC 225:2) that it is hard to discern which vegetable is from the old crop and which is new.
A common question regarding is what to do if, despite there being different growing seasons, they are available almost all year without interruption. This depends on how to understand the aforementioned Rama ("stands in the ground"). The Mishna Berura (ad loc.:18) points out that almost every vegetable has distinct growing seasons, making the Rama’s generalization about vegetables hard to understand. (Due to use of hothouses, it is now common for vegetables to be grown throughout the year.) One of his explanations is that the Rama was referring to vegetables stored in the ground for long periods. In other words, even if something does not grow all year long, if it is available throughout, we do not recite Shehecheyanu on it. When fresh produce is far superior to refrigerated produce, there is likely cause to make Shehecheyanu on the new fresh fruit (B’er Moshe V, 65). This is particularly understandable in light of the Rama’s stress that it must be noticeable whether a given fruit is from the new season or the old (see V’zot Haberacha, pg. 161).
Certainly, if a species is available only canned, one makes Shehecheyanu on new, fresh produce. Another situation where produce is available throughout the year is when it is imported from regions with different growing seasons, in which case, we do not make Shehecheyanu on either local or imported fruit. The determining factor is not the agricultural phenomenon of a new crop, but the consumers’ experience upon reaching a new season of availability.
Is the determining factor the individual consumers or general society? Regarding one who has not partaken for a long time in fruit that has been available, the Mishna Berura (225:16) says: "Although he did not eat it, others did." Thus, it is not enough that it is new for certain individuals. You ask about the opposite case, where it is new in the society where you presently find yourself, but it is not personally new to you. Teshuvot V’hanhagot (II, 151) and Halichot Shlomo (based on Rav S.Z. Auerbach’s writings) say that one who travels from a place where the season had already come to a place where there is a new season makes the beracha again in the new place. However, both require that thirty days of lack of access to the fruit must pass in the interim. In other words, there has to be a basic level of renewal both for the individual and for the society. If it has been available without a minimum interruption for either society or the individual, then the individual does not make Shehecheyanu.
The newcomer’s thirty days can be a combination of time in his place of origin and in the new place. It is not clear whether the individual’s break follows having eaten the fruit for thirty days or having access. (We should note that the original Halacha is that the beracha is on seeing the fruit, but the minhag is to make it only upon eating it (Shulchan Aruch, OC 225:3). Since we refrain from berachot out of doubt, we recommend that the traveler not make a beracha unless he spent a combination of thirty consecutive days without access to the fruit and the fruit should locally be one that is not widely available all year long. In your case, only if you spent thirty days in Israel before the avocado season should you make a beracha when it comes out.