See my answer to this post Why no 的 in this sentence?
的 1.(adjective suffix):
"的" in [姐姐给我买] [的] [衬衫] is an "adjective suffix"
"姐姐给我买的" (the one that my sister bought me) is an adjectival phrase that describes the noun "衬衫"
What shirt? The shirt that my sister bought for me
Using the adjective suffix 的 can turn a very short ...
You might be interested in these notes from ABC Cantonese on the word 添:
bei2 do1 ngo5 jat1 baat3 man1 tim1
Give me one hundred dollars more
sik6 do1 di1 tim1
Eat some more
Notes: occurs at end of sentence to indicate action is expected to be repeated; usually pronunciation with high falling tone; also ...
It's a very hamfisted example of what the book is trying to illustrate -- that 另外 and 另 can both be used to modify a verb, but that 另 is restricted to modify only monosyllabic verbs.
To answer the first part of your question: 另外/另 before 找 because it is specifically modifying the verb 找 using 另外/另 (note that you cannot use 另 for non-monosyllabic words ...