A willow, yes. But I can't help you further. Can they give you some cuttings? Willow roots easily and grows fast.

Pretty, but if that grows like a weeping willow, it'll outgrow that space in very short time....

Willows can be cut down low at the end of winter each year once well established. This does prevent flowering but in this case the specimen would be getting used as a foliage plant anyway.

Probably the most silvery willow of some size is Salix alba var. sericea (f. argentea, 'Regalis', 'Sericea'). Try searching one or more of these names followed by "price" to see if there is any current domestic availability.

Otherwise an obvious choice for silvery and olivelike is Russian olive (Elaeagnus angustifolia). But that is known for seeding around in parts of the US where it apparently feels quite at home, may turn out to be considered therefore a nuisance plant in your region as well.

I'm guessing Salix alba 'Silver Column' (basically what Embo said)

Russian-olive isn't highly invasive here (like Autumn-olive) but is very prone to a canker disease.

I'm not sure one can be very precise about the species :-) There are hundreds of willow species and many, many native ones. And the vast majority have narrow, lance shaped leaves with a slivery gray cast

Song Sparrow page linked to above calls their Arnold Arboretum origin offering S. alba sericea 'Silver Column' so implication is it is a clonal cultivar of var. sericea.