All great candidates. As you say, gaining access to such missiles is the politically tricky bit.
With the current attitudes of the Biden Administration and the Pentagon - especially towards the supply of 300 km ATACMS - I'd say that JASSM and JASSM-ER (with 370 and 925 km ranges) are off the table. But SLAM-ER has slightly less range than ATACMS (250 km) so ... maybe?
Delilah has about the same range as SLAM-ER. The missiles have been around since grunge began to fade but are still used for SEAD against Syria. At any rate, as you said, "good luck" convincing 'Bibi'
et al to provide UA with
Delilah.
BrahMos: Yep, even less chance of that.
So, that leaves RBS 15. I'm not sure where FMV is at in deploying the next-gen
Gungnir. If those RBS 15 Mk 4s are in service, then the >200 km range RBS 15 Mk.IIIs should be available. One concern is that the Mk.IIIs were co-developed by Saab Bofors and Diehl. Would that mean that Bundestag approval would be needed for transfer to UA? 'Cuz we know how long that can take

Somewhat related is the distinctly Finnish RBS-15 SF variant aka MTO-85 (
Meritorjuntaohjus 85 or anti-ship missile 85). The
Merivoimat is in the process of replacing MTO-85 with IAI
Gabriel V as the PTO 2020. Most MTO-85 were mounted on
Hamina and
Rauma class missile boats. But some were with truck-launched anti-ship missile batteries ... but would the Finns be willing to give up their Sisu SK242 launch vehicles (or will those 8x8 trucks be repurposed for ground-launched
Gabriel?) Either way, MTO-85s have a maximum range of only around 100 km.
That shorter range brings up a host of anti-shipping missiles (eg: Marte ER) but, for cruise missiles, UA needs range more than anything else right now.