Sh'lach, 15:1–16, speaks of the flour, oil, and wine that accompanied certain animal offerings. Verse 15 says, in part:
חֻקַּת עוֹלָם לְדֹרֹתֵיכֶם כָּכֶם כַּגֵּר יִהְיֶה לִפְנֵי ה׳
An eternal law for your generations; like you like the stranger shall be before God.
Rashi explains that last part:
ככם כגר ― כמותכם כן גר וכן דרך לשון עברית כגן ה׳ כארץ מצרים כן ארץ מצרים כמוני כמוך כעמי כעמך
like you like the stranger ― [means] "like you, so is the stranger". That's the way of Hebrew, [as in] "כגן ה׳ כארץ מצרים", [literally "like the garden of God like the land of Egypt", means "like the garden of God,] so is the land of Egypt[". Likewise,] "כמוני כמוך כעמי כעמך", [literally "like me, like you, like my nation, like your nation", means "like me, so are you; like my nation, so is your nation".]
The first quotation in Rashi, "כגן ה׳ כארץ מצרים", is from Lech L'cha 13:10. (The second is from Ⅰ Melachim 22:4, by the way.) The problem is that Rashi's explanation here in Sh'lach doesn't really fit the verse there in Lech L'cha, and, especially, doesn't fit with his own explanation there. The verse there says:
וַיִּשָּׂא לוֹט אֶת עֵינָיו וַיַּרְא אֶת כָּל כִּכַּר הַיַּרְדֵּן כִּי כֻלָּהּ מַשְׁקֶה לִפְנֵי שַׁחֵת ה׳ אֶת סְדֹם וְאֶת עֲמֹרָה כְּגַן ה׳ כְּאֶרֶץ מִצְרַיִם בֹּאֲכָה צֹעַר
Lot looked up and saw the whole Jordan plain, that it was all moist, before God's destroying Sodom and Gomorrah, like God's garden like the land of Egypt, as you come to Zoar.
Here, interpreting "כְּגַן ה׳ כְּאֶרֶץ מִצְרַיִם" as "like God's garden, so is Egypt" doesn't seem to make sense, since we're trying to describe not Egypt but the Jordan plain. And, indeed, Rashi interprets both "כְּגַן ה׳" and "כְּאֶרֶץ מִצְרַיִם" as comparisons to the Jordan plain, not to one another. He writes:
כגן ה׳ ― לאילנות
כארץ מצרים ― לזרעים
like God's garden ― for trees
like the land of Egypt ― for seeds
Why does Rashi cite that verse in Lech L'cha as an example of the linguistic phenomenon he's describing in Sh'lach? It isn't one, according to him.
I've looked in Mizrachi, L'vush, and Gur Arye to no avail, so turn to you.
hebrewbooks.org: one by a סנדר פרידנברג and the other by a ברוך מרדכי פרנק. Is it one of those? And then there are many "נחלת יעקב"s; do you know the author, perchance?