Using SELECTEDVALUE() for lookup in different table

Hi Community! I have a question regarding the usage of the SELECTEDVALUE() function. I have created a measure Date as in the picture below: 

Table1 contains a column, col1, that has around 130 distinct values (strings). Table2 contains a column, col2, that has around 600k distinct values (strings) and includes all values in Table1[col1]. These tables are updated daily and imported as dataflows.

I would want to be able to select a value from a slicer (containing Table1[col1]), then find that value in the Table2[col2] column and return the associated value (y) from another column, col3, in Table2. I have no relationship between the two tables (there are lots of duplicates in Table1[col1]). It seems that I cant use the function SELECTEDVALUE() when trying to search in another table with a value that has been selected in a slicer (Slicer 2). See schematic picture below:

What I have done:

In my implementation so far, I have actually another slicer (Slicer 1) that contains another column (col0) in Table1. After selecting a value (z) from that slicer, I get the associated values (x's) in Table1[col1] in another slicer (Slicer 2). But then, when selecting a value (x1) from Slicer 2, I cant seem to catch that value with the SELECTVALUE() function, to be able to search in the other table, Table2. If I instead just type the string that should have been caught by SELECTEDVALUE() in the CONTAINS() function, it works. But not otherwise...

I have tried to create creating a new table containing the UNION of Table1[col1] and Table2[col2], and implementing a measure as in picture above. This seems to find a value when using SELECTEDVALUE() function but then there is still the problem of getting the associated value from col3 in Table2.