oxVendorlist in categorylist.tpl

using: Version CE 4.8.7 / Theme Azure with myChild

Hi,
I’ d like to extend the top category navigation list with two buttons ‘manufacturerlist’ and ‘vendorlist’; linking to the lists:

[ul]
[li]By-Manufacturer/
[/li][li]By-Distributor/
[/li][/ul]

It works fine for manufacturerlist with:

[{assign var="rootManufacturer" value=$oView->getRootManufacturer()}]
<li [{if $oViewConf->getTopActionClassName() == 'manufacturerlist'}]class="current"[{/if}]>
<a href="[{$rootManufacturer->getLink()}]">[{oxmultilang ident="BRAND"}]</a></li>

I tried to do the same for vendorlist, but it didn’t work:

[{assign var="rootVendor" value=$oView->getRootVendor()}]
<li [{if $oViewConf->getTopActionClassName() == 'vendorlist'}]class="current"[{/if}]>
<a href="[{$rootVendor->getLink()}]">[{oxmultilang ident="COLLECTION"}]</a></li>

The function getRootVendor() does exist, but does not return anything (white page).

I’ve found infos about switching on ‘bl_perfLoadVendorTree’, but it is depreciated.
Any idea how to activate the function and make it available on start?
Thanks!